To be correct, resource cost reduction comes from passives in skill tree, on items it is generation, I start from poor man's variant to high end:
1. Resource aspects - rings only.
2. Rares/legendaries: resource on lucky hit - gloves, offhand, shield, resource on potion use - pants, resource generation - rings, offhand, shield.
3. Uber and regular uniques - shako, selig's amulet, tal rasha ring, lilith's ring, etc