Being a proper typist, I've always liked to keep my left hand on A-S-D-F, and have customized my games to cater to this. The number of keybinds required for Diablo3 is less than games like WoW. There are only 9 I can think of that require quick reaction time, and two of those are forced to be on your left and right mouse buttons. So coming up with something close to optimal for reaction time seemed pretty easy. Here's what I'm thinking after playing all 5 classes to 13 in the stress test:
F - Stop key. A little annoying this is even necessary, the default is SHIFT. But since Blizzard won't let you unbind move from your left mouse button, I need one of my best keybinds for this. I'm using it all the time. If you play a ranged class like Wiz or WD you'll be using your stop key a lot so you don't accidentally miss click and move toward the target rather than cast your primary ability. A bad click could mean disaster in Hardcore mode.
D - Move key. I preferred moving with the move key rather than the left click. You don't need to worry about accidentally attacking someone rather than moving (see above about Stop key). Downside is my D finger gets sore after a few hours of playing.
Ability Keybinds:
Left Mouse, Right Mouse, S, A, E, Q
Have not really settled on E and Q for last two ability keybinds, but they seem to work best while holding down F.
Use Potion - W
Toggle Items on Ground - V
Can't really think of any other keybinds I needed to use very often or with quick reaction time during the beta.