El Mahdi
Muad'Dib of the Anauroch
Let me be sure of the premise you're using:
Basically a pseudo-northern europe with a tech level equivalent to Europe between 1066 (Norman Conquest) and 1095 (the First Crusade)?
If that's correct, then I have a few notes.
First, this period is what we call the High Medieval Period. The Dark Ages are essentially the same thing as the Early Medieval Period (5th thru 9th century).
The armor of choice (if you could afford it) was Mail (not chainmail, which is a neologism created much later - the term at the time was simply "Mail"). It was usually in the form of a Hauberk (down to the knees and covering the arms), with leggings of mail (chausses), and a mail hood (coif) - with a padded Gambeson underneath and a fabric hood under the coif. Mail mittens were a later addition. There were differing kinds of Mail, most differentiated by quality (size of the rings, material used, thickness of the rings, type of "weave", riveted or not, etc.), with Kings Mail being the best (and worth a King's ransom in price).
Armors such as steel breastplates, or any armor with steel plates, wasn't developed yet (or actually re-developed yet - or we at least have no surviving samples). As far as we know, plates were not added to Mail until the late 12th into the 13th century, and wasn't common until the 14th century. This started out as what we call "transition" armor, as plates of boiled leather and steel started to be added to vulnerable points of Mail armor.
Technically, Brigandine and Coat-of-Jacks are the same thing, and as far as we know anachronistic for the period you're specifying (or at least, no surviving examples have been discovered from this period). In Europe, these also weren't developed until the late 12th into the 13th centuries, but most prominent in the 14th century.
(It may be that armor which is 100 to 200 years out of time for the period is no big deal for you, and that's cool. Just remember that for the time, it would be the equivalent of wearing modern body armor and using an M4 carbine in WWII! - as opposed to wearing a flak jacket and using an M1.)
Any such anachronistic armors, I would think, would be perfectly okay to exist if you want them to, but I would think they should either be a requested custom creation (one of a kind and veerrryyy expensive), constructed in another cultural area that may have possibly made such armor at the time (middle east, asia), or made by one of the fantasy races (Dwarves, Elves, etc.). Responses to Europeans seeing this strange armor would vary from amusement to amazement, but would most certainly be one of the extremes. It would stick out as much as a modern soldier wearing Full Plate today.
The most common armor that would be seen would simply be a padded Gambeson. This is a thick cloth armor made up of layers of cloth with their weaves running at right angles to it's neighboring layers (much like layers of kevlar in modern body armor). It was relatively inexpensive, but only relative to other forms of armor. It took a considerable amount of time and skill to make properly. Not as much as Mail, but still considerable. Also, a Gambeson was used in concert with other forms of armor. Only a fool would wear only a Mail Hauberk. Defense wise, a Mail Hauberk would provide very little protection from bludgeoning weapons, and would likely be very uncomfortable to wear without some padding underneath. A Gambeson provided fairly equal protection to all forms of attack: Bludgeoning, Slashing, and Piercing. Although other forms of Armor were significantly better at some, or all, of those.
Armors like Ringmail or Scale Mail, although possibly still encountered, would have been viewed as antique compared to Mail. They would likely be very rare, having either been handed down for generations, or taken from a foriegn warrior (scale mail especially was quite common in the middle east at this time).
Leather Armor would have existed, but probably not in the way it's commonly seen or used in D&D. Boiled leather would be almost nonexistent (last seen in Europe during the Roman Empire). Typically, leather armor would have simply been cloth (like a Gambeson), with an outer layer of leather (possibly a water proofed form).
Lamellar Armor would also be virtually unheard of in Europe (also last seen in Europe during the Roman Empire). At this time, it was only being used in the Middle East (semi-common), in Asia by Turks and Mongols (common), and early forms in Japan.
Swords.
Reference: Oakeshott typology - Wikipedia, the free encyclopedia, myArmoury.com: Oakeshott Type X Swords, myArmoury.com: Oakeshott Type XI Swords, myArmoury.com: Featured Content and Articles
From surviving examples, we believe that during the period you specify, there were no such things as "Longswords" or "Bastard" swords. There were really only two types of sword like weapons: Falchion-like blades (essentially big single edged cleavers that developed into what we call Messers by the 14th century), and "Swords". Both would have been single handed weapons (as a shield was almost always used). A "Sword" would have been a one-handed, cruciform hilt, double edged weapon with a blade of about 30" to 32", and likely have a central fuller. All swords of this time in western and northern europe were made to this general description.
Any sword that varied from the above descriptions, would have been a wholly unique and specially requested sword at this time. Also, such a sword would be wielded in combat differently than the swords of the time. Such designs would probably experience advantages and disadvantages against opponents of the day. it would be tantamount to running an experiment with an entirely new type of weapon and fighting style, with your survival in the balance. That's not something to be taken lightly, and probably why evolution and changes in weapons and armor were gradual over time. You can literally call it the Medieval Arms Race.
Some extra general notes:
The term, "Bastard Sword", was a contemporary colloquial term used for a Longsword or two-handed sword during it's time (late 13th century on). The one handed sword of the 11th century, with the a slightly longer and modified blade, would have been called an arming sword or side-sword during the same period (late 13th century on). The term "Broad Sword" wasn't used until the 17th century, when it had different meanings in different areas (in England it would have been the same as the "Longsword" of the 14th century - and called a Claymore in Scotland; in Scotland it would have been a basket-hilted, single-edged sword - which would have been called a "Backsword" in England).
There was also no weapon known as a "Shortsword" at this time. Such swords were called Gladiuses during the Roman Empire, and by other names in later time periods (13th century on). Other than the sword, all that would be carried were knives and daggers of varying sizes and names (based on region). The point at which a knife or dagger became a sword or falchion, varried from place to place, and time to time - and depended on who was carrying it or wielding it at the time, and who was making the distinction.

Basically a pseudo-northern europe with a tech level equivalent to Europe between 1066 (Norman Conquest) and 1095 (the First Crusade)?
If that's correct, then I have a few notes.
First, this period is what we call the High Medieval Period. The Dark Ages are essentially the same thing as the Early Medieval Period (5th thru 9th century).
The armor of choice (if you could afford it) was Mail (not chainmail, which is a neologism created much later - the term at the time was simply "Mail"). It was usually in the form of a Hauberk (down to the knees and covering the arms), with leggings of mail (chausses), and a mail hood (coif) - with a padded Gambeson underneath and a fabric hood under the coif. Mail mittens were a later addition. There were differing kinds of Mail, most differentiated by quality (size of the rings, material used, thickness of the rings, type of "weave", riveted or not, etc.), with Kings Mail being the best (and worth a King's ransom in price).
Armors such as steel breastplates, or any armor with steel plates, wasn't developed yet (or actually re-developed yet - or we at least have no surviving samples). As far as we know, plates were not added to Mail until the late 12th into the 13th century, and wasn't common until the 14th century. This started out as what we call "transition" armor, as plates of boiled leather and steel started to be added to vulnerable points of Mail armor.
Technically, Brigandine and Coat-of-Jacks are the same thing, and as far as we know anachronistic for the period you're specifying (or at least, no surviving examples have been discovered from this period). In Europe, these also weren't developed until the late 12th into the 13th centuries, but most prominent in the 14th century.
(It may be that armor which is 100 to 200 years out of time for the period is no big deal for you, and that's cool. Just remember that for the time, it would be the equivalent of wearing modern body armor and using an M4 carbine in WWII! - as opposed to wearing a flak jacket and using an M1.)
Any such anachronistic armors, I would think, would be perfectly okay to exist if you want them to, but I would think they should either be a requested custom creation (one of a kind and veerrryyy expensive), constructed in another cultural area that may have possibly made such armor at the time (middle east, asia), or made by one of the fantasy races (Dwarves, Elves, etc.). Responses to Europeans seeing this strange armor would vary from amusement to amazement, but would most certainly be one of the extremes. It would stick out as much as a modern soldier wearing Full Plate today.
The most common armor that would be seen would simply be a padded Gambeson. This is a thick cloth armor made up of layers of cloth with their weaves running at right angles to it's neighboring layers (much like layers of kevlar in modern body armor). It was relatively inexpensive, but only relative to other forms of armor. It took a considerable amount of time and skill to make properly. Not as much as Mail, but still considerable. Also, a Gambeson was used in concert with other forms of armor. Only a fool would wear only a Mail Hauberk. Defense wise, a Mail Hauberk would provide very little protection from bludgeoning weapons, and would likely be very uncomfortable to wear without some padding underneath. A Gambeson provided fairly equal protection to all forms of attack: Bludgeoning, Slashing, and Piercing. Although other forms of Armor were significantly better at some, or all, of those.
Armors like Ringmail or Scale Mail, although possibly still encountered, would have been viewed as antique compared to Mail. They would likely be very rare, having either been handed down for generations, or taken from a foriegn warrior (scale mail especially was quite common in the middle east at this time).
Leather Armor would have existed, but probably not in the way it's commonly seen or used in D&D. Boiled leather would be almost nonexistent (last seen in Europe during the Roman Empire). Typically, leather armor would have simply been cloth (like a Gambeson), with an outer layer of leather (possibly a water proofed form).
Lamellar Armor would also be virtually unheard of in Europe (also last seen in Europe during the Roman Empire). At this time, it was only being used in the Middle East (semi-common), in Asia by Turks and Mongols (common), and early forms in Japan.
Swords.
Reference: Oakeshott typology - Wikipedia, the free encyclopedia, myArmoury.com: Oakeshott Type X Swords, myArmoury.com: Oakeshott Type XI Swords, myArmoury.com: Featured Content and Articles
From surviving examples, we believe that during the period you specify, there were no such things as "Longswords" or "Bastard" swords. There were really only two types of sword like weapons: Falchion-like blades (essentially big single edged cleavers that developed into what we call Messers by the 14th century), and "Swords". Both would have been single handed weapons (as a shield was almost always used). A "Sword" would have been a one-handed, cruciform hilt, double edged weapon with a blade of about 30" to 32", and likely have a central fuller. All swords of this time in western and northern europe were made to this general description.
Any sword that varied from the above descriptions, would have been a wholly unique and specially requested sword at this time. Also, such a sword would be wielded in combat differently than the swords of the time. Such designs would probably experience advantages and disadvantages against opponents of the day. it would be tantamount to running an experiment with an entirely new type of weapon and fighting style, with your survival in the balance. That's not something to be taken lightly, and probably why evolution and changes in weapons and armor were gradual over time. You can literally call it the Medieval Arms Race.
Some extra general notes:
The term, "Bastard Sword", was a contemporary colloquial term used for a Longsword or two-handed sword during it's time (late 13th century on). The one handed sword of the 11th century, with the a slightly longer and modified blade, would have been called an arming sword or side-sword during the same period (late 13th century on). The term "Broad Sword" wasn't used until the 17th century, when it had different meanings in different areas (in England it would have been the same as the "Longsword" of the 14th century - and called a Claymore in Scotland; in Scotland it would have been a basket-hilted, single-edged sword - which would have been called a "Backsword" in England).
There was also no weapon known as a "Shortsword" at this time. Such swords were called Gladiuses during the Roman Empire, and by other names in later time periods (13th century on). Other than the sword, all that would be carried were knives and daggers of varying sizes and names (based on region). The point at which a knife or dagger became a sword or falchion, varried from place to place, and time to time - and depended on who was carrying it or wielding it at the time, and who was making the distinction.
