I personally enjoy a "cloth mousepad with a rubber bottom" for my infrared mouse, for a couple reasons really.
-It's soft and comfortable when I rest dangling fingers while not in heavy use (mainly pinky)
-It's warm as opposed to a cold desk
-It's clean, and easy to wash. Smooth desks usually get dusty/dirty/scummy over time
-Without a mousepad, dirt easily builds up under the small mouse "feet"
-No mouse pad will scuff up your desk over a long period of use
Yes perhaps I'm just being anal, but it's the little things in life right? And besides mousepads are super cheap and last a few years before they wear out and get fuzzies/lint ball buildup.
I'd recommend one of the oversized slim mousepads, I'm currently using a Steelseries (some available @ Blizzard store, 12" X 10.5"). You don't have to get from Blizzard, you can get a decent mousepad with your favorite picture/game from just about computer outlet. A picture / game scene you like is just going to be the key
I got the Steelseries because I was ordering gifts at the time, and I'd say it was good quality. Spilt beer all over it a couple times and it washes out nicely without screwing up the fabric