Some food for thought here.
I've long pondered a DR-based armor system, but I'm persuaded to refrain from such large changes. Instead, I've stolen several other ideas from this thread (thanks guys, hehe

), and written up a treatment of the subject for my new campaign. This is mostly a rehash of existing ideas, modified for my house rules. Criticism is welcome.
--------------------
MOVEMENT IN ARMOR
Base movement rates for wearing medium and heavy armor in the PHB are unduely penalized. Under this house rule, base movement speed (walking) is unaffected by armor, as long as the wearer has the appropriate armor feat. However, speeds faster than walking are limited as follows: medium armor imposes a maximum movement rate of Run (x3) and heavy armor limits the wearer to Hustle (x2) speed.
ARMOR FEATS
Armor Focus (General, Fighter)
You excel in the use of a particular type of armor.
Prerequisite: appropriate armor feat (light, medium, heavy)
Benefits: Choose one specific type of armor. Your armor check penalty is reduced by 2 and the maximum Dexterity bonus is raised by 1 (to a maximum of +4) with this armor. The armor check penalty cannot be lowered below zero.
Special: The character can gain this feat multiple times. Its effects do not stack. Each time the character takes the feat, it applies to a new armor type.
Armor Mobility (General, Fighter)
You are an expert at moving in custom-fitted armor.
Prerequisites: +5 BAB, Armor Focus, Mobility, custom masterwork armor
Benefit: Choose an armor type with which you already have the Armor Focus feat. As long as you are wearing masterwork, custom-made armor of this type, your armor check penalty is reduced by 4 and the maximum Dexterity bonus is raised by 3 (to a maximum of +6). These effects do not stack with the Armor Focus feat. The armor check penalty cannot be lowered below zero
Special: The character can gain this feat multiple times. Its effects do not stack. Each time the character takes the feat, it applies to a new armor type.
CRITICAL DEFENSE
The very purpose of worn armor is to provide protection to vital areas of the body, and should provide some measure of protection against critical hits that cannot be gained with non-armor AC bonuses.
This house rule defines an addition property to armor called critical defense. The critical defense value raises an opponent's critical confirmation DC by the listed amount. As a rule of thumb, any armor or natural armor bonus provides critical defense at ½ the AC bonus. This includes the appropriate enhancement bonuses, thus
+5 full plate has an effective critical defense of 6. The resulting armor list looks like this:
Armor Table
Code:
[color=gold] Armor Max Check Crit
Armor Cost(gp) Bonus Dex Penalty Def Weight
-------------- -------- ----- --- ------- ---- ------
[i]Light armor[/i]
Padded 5 +1 +8 0 0 10 lb.
Leather 10 +2 +6 0 1 15 lb.
Studded leather 25 +3 +5 -1 1 20 lb.
Chain shirt 100 +4 +4 -2 2 25 lb.
[i]Medium armor[/i]
Hide 15 +3 +4 -3 2 25 lb.
Scale mail 50 +4 +3 -4 2 30 lb.
Chainmail 150 +5 +2 -5 2 40 lb.
Breastplate 200 +5 +3 -4 2 30 lb.
[i]Heavy armor[/i]
Splint mail 200 +6 +0 -7 3 45 lb.
Banded mail 250 +6 +1 -6 3 35 lb.
Half-plate 600 +7 +0 -7 3 50 lb.
Full plate 1,500 +8 +1 -6 4 50 lb.
[/color]
Note that Keen weapons can bypass the effect of critical defense. Keen weapons ignore critical defense values equal to or less than their enhancement bonus. Thus, a
+2 keen dagger would ignore any critical defense of 2 or less.