Dex adds to AC, Initiative, ranged attack roles and melee attack roles if you have Weapon Finesse - Note, all Rogues automatically get Weapon Finesse at 1st level.
There are several feats / class abilities that allow you to apply Dex bonus to melee weapons. Notablly the Rogue's Finesse training, and off the top of my head there is the Slashing Grace feat (which allows you to select any one slashing weapon of suitable size).
Also, not as reliable and requires you to find them, there are weapons with the Agile enchantment which does the same.
Yup, works fine for my thief/fighter with bastard sword:
http://www.aonprd.com/FeatDisplay.aspx?ItemName=Slashing%20Grace