Third Class Announced: Wizard
This morning at the BlizzCon 2008 opening ceremony, the third class for Diablo III was announced -- the Wizard! These ranged casters are "all about channeling the powers of the universe ". Blizzard has given us access to the initial gameplay video that was shown during the ceremony; check it out!
Also make sure to view all of our new Diablo III screenshots from BlizzCon, they make it pretty clear that the team is making some forward progress on the game.