I think it depends on what you want. Wired or Wireless? Trackball or Regular? Programmable buttons? Adjustable DPI?
 
Wireless, regular, two buttons and a scroll wheel. small enough for my entire hang to cover (not too hard, my hands are large) take double A batteries.....made of plastic? I can't think of anything else
 
IMO stay away from Razer. My last two mice have been Razer (in fact the one I'm currently using is a Razer Lachesis) and both have been shite.
 
Necro-fucking-bumping.

Buying this one right nao:

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Razer Naga Molten Addition. Nuff Said.

I have one and they seem pretty good for anything especially for your key bindings on tf2 :).
 
Yes! (I mean, when you're playing for 5 hours straight your palms are getting wet for sure).
Holy mother of God, that's an amazing invention. Where can you buy one of those at, I'm getting rid of the G500 on my shopping cart on Newegg and putting that in there.