Razer Destructor- It's an awesome mat. Large surface area and flush to the table resulting in no annoyance to the wrist. It also has a very fine grain to it which result in perfect tracking.
I was not expecting much when I bought it, however have been very pleasantly surprised.
I've use an Ice Mat before the Razer and that was awful in comparison- raised, noisy and cold to the touch. Quite uncomfortable.