Weapons of Masterwork Quality provide a +1 bonus to attack rolls, but not to damage rolls.
Magically enhanced weapons provide a +1 bonus to damage as well. (Masterwork quality is assumed.)
Adamantine: Mined from rocks that fell from the heavens, this ultrahard metal adds to the quality of a weapon or suit of armor. Weapons fashioned from adamantine have a natural ability to bypass hardness when sundering weapons or attacking objects, ignoring hardness less than 20.
Adamantine has 40 hit points per inch of thickness and hardness 20.
Cold Iron: Mined deep underground and known for its effectiveness against demons and fey creatures, is forged at a lower temperature to preserve its delicate properties.
Cold iron and steel have 30 hit points per inch of thickness and hardness 10.
Mithral: A very rare silvery, glistening metal that is lighter than steel but just as hard. An item made from mithral weighs half as much as the same item made from other metals. Called True Silver by the Dwarves, mithral weapons count as silver for the purpose of overcoming damage reduction.
Mithral has 30 hit points per inch of thickness and hardness 15.
Per table 7-12 on page 175:
Normal light weapons (dagger) typically have 2 hit points, one-handed blades (sword, rapier) 5 points, and 2-handed blades (greataxe, greatsword, longspear) 10 points, etc; add 2 points of hardness and 10 hp per +1 magic enchantment.
(i.e. a normal 2-handed greataxe with a metal haft would be 10/10, made of adamantine would make it 20/15, and a +1 enchantment on top of that would be 22/25.)