I'm absolutely amazed that not one person mentioned or uses the CS Hyde mouse pad line, which is the BEST surface you can get for a mouse. It lasts practically forever. I've had mine for 3 years now. I use it 8+ hours every day, with HEAVY usage (productivity + FPS gaming). It has not worn out, and all I simply do is oil it up with baby oil once a week. pwnage!
Steelseries i-2. Love it. I came from a regular $1 cloth pad to this. Takes some time to get used to, but you love it in the end. When going back to a cloth pad, It feels so sluggish/too much friction.
I use paper, funnily enough! I keep a stack of sheets on my desk next to the rig. It's high quality printer paper with a nice sheen. Absorbs sweat and when you're done with it, you chuck it away! Almost like beer cans or women...
Works great - I started using it years ago when ball mice were still the only option, as I found it kept the ball clean by absorbing sweat. Now it's all I use. Old habits, I guess.