Leave it to fans to pay close attention. The folks from DIII.net, a Diablo III fan site, have dutifully noted all the skill trees as they appeared in the playable version of the game at BlizzCon. They're furthermore presented them with a mocked up graphical interface.

These are not actual game skill tree screenshots; Blizzard has never released those, but these are exactly accurate for all the skill names, positions, and pre-reqs as of the BlizzCon 2009 demo build. See the Monk Skills, Witch Doctor Skills, Barbarian Skills, and Wizard Skills pages in the wiki for full details about every skill and spell in the game.