Ok I'm done with my chores so a bit more delving on the situation of our knight:
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Milita member: 2.5 hp (commoner 1), Attack +0 (BAB), average damage 3.5 (1d6 weapon), AC 13 (padded, heavy shield). A surviving militia member does 0.7 damage per round to either type of knight (20% chance to hit times average damage).
Professional soldier: 5.5 hp (warrior 1, nonelite, +1 Con from standard array), Attack +2 (BAB, +1 Str), average damage 5.5 (1d8 weapon), AC 13 (same as militia. A surviving soldier does 1.65 damage per round (30% chance to hit).
New knight: 11 hp (warrior 2, +1 Con from standard array), Attack +3 (BAB, +1 Str), average damage 11 (lance, charge), AC 17 (mail, heavy shield), warhorse, Ride-by Attack. A new knight has a 48% chance to take out a soldier on a single hit (55% chance to hit, only survives on a damage roll of 1), or a 55% for a militia member (can't even survive on a 1).
Experienced knight: 16.5 hp (warrior 3), Attack +6 (BAB, +1 Str, Weapon Focus, masterwork), average damage 11, AC 17, etc (still no Spirited Charge). An experienced knight has a 61% chance to take out a soldier on a single hit (70% chance to hit), or 70% for a militia member. Suffers the same damage as a new knight.
New knight vs. militia:
3-on-1: New knight will fall in 6.41 rounds, killing 3.53 militia.
2-on-1: New knight will fall in 10.8 rounds, killing 5.96 militia.
1-on-1: New knight will fall in 34.9 rounds, killing 19.2 militia.
New knight vs. soldiers:
3-on-1: New knight will fall in 2.65 rounds, killing 1.27 militia.
2-on-1: New knight will fall in 4.39 rounds, killing 2.11 militia.
1-on-1: New knight will fall in 12.9 rounds, killing 6.18 militia.
Experienced knight vs. militia:
3-on-1: Experienced knight will fall in 10.3 rounds, killing 7.17 militia.
2-on-1: Experienced knight will fall in 18.1 rounds, killing 12.7 militia.
1-on-1: Experienced knight will fall in 78.6 rounds, killing 55.0 militia.
Experienced knight vs. soldiers:
3-on-1: Experienced knight will fall in 4.19 rounds, killing 2.57 militia.
2-on-1: Experienced knight will fall in 7.21 rounds, killing 4.41 militia.
1-on-1: Experienced knight will fall in 25.8 rounds, killing 15.8 militia.[/sblock]
A group of 2nd or 3rd level knights attacking in a tight formation to minimize their exposure to multiple attacks will
mow through their opponents (opponents who use reach weapons that allow multiple ranks to attack will significantly shift the balance in the other direction, as will knights who get surrounded or attack on their own).
Sorry, no more sidetracks.

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Ok so, some quibbles:
1) I don't think a 1st level commoner is really accurate for a militia.
2) I definitely don't think a knight would be a Warrior class in most cultures, an Aristocrat is a good fit as I said before but a couple of levels of Fighter is likely if they are meant to actually be knights in more than name (title) only.
First on point One (please forgive another long winded digression here..):
While I know this complicates matters a bit more than most people will bother with in their campaigns, for purposes here of the context of the Knight, depending on the region and the specific time you are depicting in your campaign, and whether it is an urban or rural militia, realistically in 3.5 rules a Militia soldier would be a multiclassed character.
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I know it's a popular image of the middle ages that you basically had knights on the one hand and peasant rabble on the other, but things are always more complex when you look into history.
In fact with the caveat that it's always dangerous to generalize about history in general and about Medieval Europe in particular, I think this Monty Python image is largely a myth. There were plenty of peasant rabble of course but those type of lowly serfs didn't usually fight. Militia were usually made up of slightly wealthier peasants and burghers.
Militia get a bad rap in DnD I think. Historically they actually tended to be pretty well trained and were usually pretty tough. Untrained common peasants really didn't fight that much in the period we are talking about (11th Century - 14th, the heydey of the knight) Anything after that and you had militia who were so good they could demand top dollar as mercenaries, such as the Genoese crossbowmen, Welsh longbowmen, Irish Galloglaich, German Landsknechts, Catalan Almogavars or Swiss halberdiers etc. etc.. This doesn't mean they weren't commoners, which they were, and many were still in fact peasants (or burghers) in their day job, but to be in the militia meant that regular training was done, and militias were routinely mustered and had to be tested in all kinds of skirmishes, sieges and small engagements. This amounted to skill and experience when push came to shove.
Anything before our Knightly period was a mix, there were some untrained peasants sometimes pushed into battles but they did abysmally and were soon replaced by more professional soldiers. This is why Alfred the Great rebuilt the Anglo Saxon fyrd system in Britain because he found ceorls were useless in combat. It took years of drilling and retraining before they eventually did recover their ability to provide some resistance against the Vikings.
Before 1100 you had either warriors still trained in traditional tribal warfare, like the Scottish Highlanders or the Anglo Saxon Fyrd or the Viking Baendir, or the the Rus Voi (rural militia), as well as en even tougher emerging urban militia such as in the Kieven Rus towns, the Italian City states and the Hanse cities etc. All of whom were considered pretty formidable - the Rus urban miltia were able for example to fend off the Mongols at Novgorod (as were Czech militias in Bohemia), no mean feat considering that the Mongols were able to largely annihilate the cream of European knighthood at the battles of
Leignitz in Poland and Sajo river in Hungry. (In fact after the knightly army was defeated in Hungary it was the militias in the little towns who successfully fought off the Mongols in the extended guerrila campaign which followed).
Their kit would be a little better, they should have decent armor and from circa 1150 AD would almost always have high-energy missiles like heavy crossbows or (more rarely) longbows. So the knights would not actually be immune to attack even though they are using reach weapons.
A common point of confusion here is due to a major change in the economy of iron in Europe around the time of the rise of the Knight. In fact there have been some good books written on the idea of the link between these two events like [ame="http://www.amazon.com/Knight-Blast-Furnace-History-Metallurgy/dp/9004124985/ref=sr_1_1?ie=UTF8&qid=1232228530&sr=8-1"]this one[/ame] which I would love to read but can't afford the $375 for!!) To make a long story short the [ame="http://en.wikipedia.org/wiki/Cistercians"]Cistercian Monks [/ame] went all over Europe in the first half of the 12th Century spreading the technology of the overwash water wheel and the windmill, thinking that this would bring about a Golden Age of prosperity. One of the things it did bring about was automated bellows and [ame="http://en.wikipedia.org/wiki/Trip_hammer#Medieval_Europe"]trip hammers[/ame] which allowed for the production of relatively cheap homogeneous steel of excellent quality in very large quantity.
So wheras during say the early Middle Ages / Dark Ages / Migration period back in the early Viking times or the rise of the Franks, a well made sword or armor were worth more than whole villages, by the time Knights roll around, probably not coincidentally, armor had become much cheaper and some kind of protection was fairly common for professional soldiers, mercenaries, and yes even militias.
Pikes (long spears) appeared later in the 14th century, used by well trained specialists, as were weapons like Halberds, Bills and true-two handed swords which were all usually wielded by elite experts called "Dopplesoldners" who were paid double the normal rate for soldiers.
Very generally speaking, I may be making an incorrect assumption but to me, if a guy has been training in the militia for 10 or 15 years, has been in at least a half dozen raids, skirmishers or sieges, maybe one or two actual wars, and has probably killed more than a few people in combat, he's probably not still a 1st level commoner. Similarly an actual professional soldier from a veteran company (like the Catalan Grand Company mentioned above) in this period was a hard bitten killer who would have been in scores if not hundreds of combats and would in fact be a lot more like a typical PC, so something like a 1st - 3rd level fighter or 2nd - 4th level warrior on average.
To put it into perspective, a Viking was a commoner and essentially a peasant: a farmer or a fisherman who went on trading voyages and occasional raids in the summer. Many were part of the local militia or
leiðangr, some went on to join armies or professional raiding bands (Vikinglegs) such as the famous Jomsvikings). We know Vikings were pretty tough, probably not 1st level commoner material...
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Typical rural militia might be a 1st-3rd level commoner (depending on age)
and a 1st level warrior, wheras in a city or certain specific rural areas (like Switzerland) you might have a multiclassed character who is a 1st or 2nd level commoner or expert,
and a 1st or 2nd level fighter. The latter in particular would be fairly well equipped, again depending on the region and the time period, probably with something like mail hauberk, a helmet and a shield, a spear or a crossbow, as well as a sidearm like a sword, a hammer, an axe or a mace (more on these in a later post).
I guess all this depends a lot on the philosophy of your game and where and when you set it of course.
On Point Two
Because they effectively were specialized killers trained in many cases from early youth, I think a combatant knight would be a Fighter, though I guess you could make an argument for their being a Warrior since they didn't typically have a lot of discipline in this period.
Knight was both a title and a military rank, the former going back to Roman times with the Equestrian ("Equites") rank of junior nobility. As in Roman times, someone might frequently have the social rank of 'Knight' (or chevalier, reitter, caballero etc.) but not actually be a fighter at all, or perhaps be only nominally a fighter who would go to battle only when they had to. These would be covered by the Aristocrat Class. The actual serious fighting knight though was a professional lifelong occupation, very much done with constant formal training and tests of mettle on both the battlefield and the tournaments (and it's worth noting, tournaments in this period 1100-1300 AD were really rough affairs, more like small controlled wars, in which people usually died and men's fortunes were won or lost as they were captured and held ransom in the course of bloody pitched battles)
Anyway I don't mind the seques at all I think they are interesting and fun to talk about, so by all means lets continue this discussion about what class and level a knight should be, the militias etc. we can just keep the lengthy digressions in the sblocks and meanwhile move on into the ideas of how to customize knights a bit further from the basic template.
For a little more insight into the origins of European Medieval militias check out these articles on some early medieval tribal and urban assemblies: the Slavic Veche, the Norse Leidang and the Ting, and the Anglo-Saxon Fyrd
http://en.wikipedia.org/wiki/Veche
http://en.wikipedia.org/wiki/Fyrd
http://en.wikipedia.org/wiki/Thing_(assembly)
http://www.regia.org/warfare/fyrd2.htm
G.
EDIT: Note in the Wiki on the Norse Lidang it mentions that records from the 12th - 13th century show that militia were under obligation to report with the following gear: helmet, mail hauberk, shield, spear and sword