#2 - May 11, 2011, 9:29 p.m.
Wizard uses Arcane Power which regenerates quickly on it's own, and has a finite cap. The witch doctor has Mana which regenerates slowly, and uses skills to actively recover it. They're fairly similar in concept but the fast regen of Arcane Power plays well into the burstyness of the wizard.
The demon hunter resource is still under wraps, although the basic premise has been talked about quite a bit.