I'm using this teeny (my hand hurts using it after a while) wireless Logitech mouse, and I need to upgrade (after seeing my friends cool mouse and after playing Tribes...).

I have a few questions though:
Wireless or wired?
What DPI should I be looking at?
What brands are good?

I'd much prefer a wireless mouse, I haven't noticed much of a problem with this mouse being wireless (like, no interference) but if it's better to go wired I will.

Wired damnit
3500
DeathAdder 3500 its got a gold connector majigger and a braided cable.
People call my hands "sausages" so it should do well for you.

Wired.
DPI isn't important.
It is all personal preference, but my favorite mouse is the Intellimouse Explorer 3.0.

A lot of people will say wired over wireless for gaming but wireless is fine too as long as you get a good one like the Razer Mamba. The biggest annoyance with them is the battery life.

Personally though I really like the Logitech G400. You really should try to hold any potential candidates before you buy it. I bought a Logitech G9 without holding it and the right side was just awful. Very uncomfortable.

As for DPI, it's not a big deal. I'm using mine at 1600 DPI and that may even be a little bit too high for gaming. My desk is just too cramped to lower it.

I'm rather fond of http://www.newegg.com/Product/Product.aspx?Item=N82E16826104321 I've gone through lots of mice over the years and this one is by far my favorite so far. Decent battery life, and it comes with a recharging cord that you plug into your pc so you can play while you charge it.

That's almost exactly the same as mine, except mine is wired with less extra buttons.

I think it's mostly down to personal preference, like what shape fits your hand and how many buttons you need. DPI isn't as important as they advertise, so I wouldn't pay extra for a mouse just because it claims to have a super high DPI.

Got a G500. Old but awesome.

I am using the http://www.amazon.com/Razer-Laser-Gaming-Mouse-RZ01-00280100-R3/dp/B002MPPRPO/ref=sr_1_1?ie=UTF8&qid=1330298322&sr=8-1. I love it. Feels nice, plus the 12 thumb buttons are so helpful when in game

I love my Microsoft X8.

The Logitech MX518 is an oldie but goodie. What is the new model number for it now? I can't keep track.

That's the one I have, I love it. The G400 that Lord Crow mentioned is supposed to be the MX518's successor IIRC.

Whatever you get, having buttons or a switch on the side of the mouse to change DPI settings on the fly is very useful. Whenever I am playing BF3 I keep it at the medium setting, but when I hop in a tank or jet I quickly hit the button to switch to ultra-high DPI, making it possible to aim the tank and turn the jet very quickly.