I've got a razer diamondback. Wouldn't buy any other brand of mouse now that i've fallen for these.
On-the-fly sensitivity adjustment means you can change it in 10% increments, even in the middle of a game. 7 buttons, each one fully customisable. Pretty lights. Teflon feet as standard. Did I mention the pretty lights?
6 foot cable, gold plated connector, 100hz polling frequency (means you save about 7ms on anything you do with it). Software even lets you turn off the damn annoying "acceleration" that you get with standard mice.
get a gaming grade mousemat to make best use of it, although the precision of an infra-red sensor is unbeatable.
One thing to look out for... don't think the mouse is broken because there's no light from the bottom, and then look into it... its infra red, it'll burn your eyes!