There are the regular wheels, and then there is a series of rollers rotated 90 degrees from the original wheel. Depending on what type material of rollers you use, you can get foward traction and still have an easy turning capability.
If your drive system is made of all omni-wheels, then you'll be pushed to the side really easily.
There is a drive system called "holonomic drive" where the omni-wheels in the corners are rotated 45 degrees from the drive base. Each wheel will have to be individually driven by separated motors. Depending on which way the wheels are being driven, you can strafe and drive in a circle while facing the same way. This is an omni-directional drive.
