pretty much any mousepad will do.
however I'd recommend an everglide or ratzpad like Quad said.
When you're gaming, you want precise movements with a little friction in the pad.
The tracking doesn't matter since its optical, but you want the mouse to move smoothly and accurately. I don't think any desk can produce the friction you need...plus you gotta keep it clean. These two pads don't slide around on the desk like an ordinary pad or mat will, and they provide a good amount of friction.
Good luck.