I swear by my Logitech MX518.
Razer makes some highly regarded gaming mice.
Edit: I forgot you said why. Here are some general things to look for in a mouse you want to game with:
-High dpi (dots per inch) -finer control over movement. Usually at least 1600 dpi for a gaming mouse.
-Light (or variable) weight - quicker movement
-Lots of buttons - programmed buttons on your mouse can be easier than key combinations
-Scroll wheel with "notches", not free spinning - makes for switching between weapons and the like easier
-Wired - if you get really serious you probably want a wired mouse to avoid any lag. Wired mice also usually weigh less.