In an attempt to make there be a bit more variety in possible selections of equipment, I'm making a few changes to weapons and armor.
Adamantine armor damage reduction is increased, as follows: light armor gets DR 5/50%, medium armor DR 5/-, and heavy armor DR 10/-. However, see also the changes to adamantine weapons.
elven chain - The elves like their light armor, and have managed to devise mithril chainmail that is statistically identical to a mithril breastplate.
Dwarves, on the other hand, craft some superior quality adamantine armors. However, for reasons known only to themselves, they disdain medium armor.
dwarven chain - masterwork adamantine chain shirt with a +5 armor bonus, 6,100gp
dwarven plate - masterwork adamantine full plate with a +9 armor bonus, 21,500gp
Dragonhide armors are generally of superior quality, but also tend to be quite expensive - as they require either a live dragon and lots of time, or a dead dragon. Note that these armors are already considered masterwork, and the bonus from that is included in the listed stats.
dragonhide armor: Despite its name, dragonhide armor more closely resembles a very fine scale mail. In order to procure the scales needed for dragonhide armor, you need a live dragon (any size), or a dead dragon at least as large as you are.
light armor, 15lbs, AC +3, max dex +7, armor check -0, spell failure 10%, market value 8,000gp
dragon scale mail: uses larger scales, typically a few inches across. Requires a live dragon at least as big as you are, or a dead dragon at least one size category larger.
medium armor, 30lbs, AC +6, max dex +4, armor check -2, spell failure 20%, market value 11,000gp
dragon plate armor: requires a live dragon two sizes larger than you, or a dead dragon three sizes larger. Dragon plate armor is very rare, and usually heavily enchanted.
heavy armor, 50lbs, AC +9, max dex +2, armor check -4, spell failure 30%, market value 17,000gp
Silver weapons: When fighting a creature whose damage reduction works by instantaneous healing, silver weapons count as having an extra +3 for purposes of overcoming damage reduction. This includes lycanthropes (normally DR 10/+3), as well as many forms of demon and undead.
In addition to the alchemical silver weapons described in the DMG, one can make enchanted weapons out of solid silver. Such weapons cost an extra 4,000gp to create, and must be enchanted to at least +1. However, they do not suffer the damage penalty of an alchemical silver weapon. Also, such weapons conduct magic, and can be used to deliver melee touch attack spells.
Cold Iron weapons: When fighting a creature whose damage reduction works by magically reducing the impact, cold iron weapons count as an extra +2 for purposes of overcoming damage reduction. This includes fey, some magical beasts, and some forms of demons and undead. Also, cold iron is disruptive to creatures held together by magic. This includes most magical beasts, many elementals, some fey, constructs, and undead. If you successfully deal damage to such a creature with a cold iron weapon, add an extra 1d6 damage; on a roll of 6, add in another 1d6, and so on.
Adamantine weapons: When fighting a creature whose damage reduction works by simply being that well armored, adamantine weapons reduce the amount of damage reduction by 10. This includes object hardness, dragons, most constructs, some elementals, and the damage reduction granted by adamantine armor. Also, adamantine weapons still have their normal advantage of being much more durable than weapons made from other materials.
If you're fighting something with damage reduction based off of simply ignoring injury (for example: high level barbarians), or not being there when you hit (for example: skeletons and the gaseous form spell), no special weapon material is going to help you.
Holy weapons: Holy weapons count as an extra +1 for purposes of overcoming damage reduction against any creature that their bonus damage would apply to. Some holy weapons adapt to the beliefs of their wielder, but many are more limited. Common limitations are: only followers of a deity that channels positive energy, only followers of a particular pantheon, only followers of a particular deity.