Righto mate, there are 2 possibilites i beleive there are in gaming mice. Ones for either low sensitivity gamers or high sensitivity gamers.
Low sensitivity is where you move the mouse a lot further to cover the same distance and therefore you need stability. One of the best mice for this is a very simple intellimouse (probably the most widely used mouse by top gamers):
Intellimouse 3.0
There is also a steelseries special edition intellimouse, but these are quite rare as far as iI beleive.
Razer has made a mouse with the aid of microsoft called the Habu:
Microsoft Habu
The last option is a Logitech MX518 which is still one of the best mice out there for only £15:
Logitech MX518
Then there are the mice for high sensitivity. These need to be small and have the best tracking devices as you only move them a very short distance. This is what many people believe is best for gaming. However if you ask any top gamers they will ALL play with a low sensitivity. For high sens however your best bet is a razer mouse, although they do break after about a years good use, choose from the below (I use a Diamondback 3G):
Razer Diamondback 3G
Razer Deathadder
Razer Lachesis
Dont bother with any changeable weights or anything that makes you spend more than you need. I had a Microsoft Sidewinder with changeable weights and grips and got rid of it within the month. You need to find out what sensitivity suits you and then buy the mouse to match this. I know all this from playing CSS at a very decent level for 6 years
Oh and also go for a wired mouse all the time as wireless can cause lag between moving the mouse and the computer percieving this information, which means your crosshair will move after youve actually moved the mouse.