What Mouse is best for gaming?

I've been browsing the main net sites that would sell Mice (of the digital variety) in the UK and I really can't tell what's the best option for me.

I'm spending around £600 on my rig and I won't have much money left after that, so does anyone know of a good gaming/budget USB optical gaming mouse?

Thanks in advance.

I also got it because I got it for $40 which was a steal and half. Killfox

This raises an interesting question:

Where the hell did you find a G9 for $40?