noone mentioed Razer? IMHO, the Razer mice are AWESOME. I have only used the Copperhead from Razer, but the Diamondback looks to be almost as good. The copperhead is so sensitive, you can use it perfectly from around 3mm off the surface (you actually dont notice any loss of sensitivity 3mm off the mouse pad)
it takes a little getting used to the shape, and may not be perfect for everyone, but I love it, and I would have to say it is the best mouse on the market.
That said, the G5 and MX518 are the next best to me, and not bad mice at all.