[Lil' Lavery]

There are plenty of wheel options out there. Consider what your design priorities are, and then select wheels to match them.
http://www.andymark.com/Wheel-s/229.htm
http://www.vexrobotics.com/vexpro/wheels-and-hubs
http://banebots.com/c/WHB
http://www.robotmarketplace.com/prod...eels_main.html

Originally Posted by Ether

You don't need 6. You can do it with 4.

You can "do it" with 3, actually. Assuming by "do it" you mean transverse in two different axes independent of any frame rotation.