ASUS P5Q C&P5Q E&P5Q PRO

P5Q-C - Supports DDR2 and DDR3, but not at the same time.
P5Q Pro - DDR2 memory, Crossfire support.
P5Q-E - DDR2 memory, Crossfire support, 1 x PCI Express x16 slot at max. x4 link, dual Gigabit LAN, best cooling.

They're all good. Select one based on your requirements, but I'd probably stay away from the P5Q-C because supporting DDR2 and DDR3 usually doesn't provide optimal stability.