One mouse I can recommend is the Logitech MX Revolution. That mouse is pretty nice and would easily compliment the aluminum iMac .
I have one. Best mouse I've ever used.
My Mighty Mouse that came with my Aluminum iMac broke (scroll ball) so I got a new one. Then the scroll ball on that got clogged up too... so I felt it was time to buy a different mouse that WOULDN'T suck balls (pun intended).
So I bought the MX Revolution (Which is also on it's second model since the first one they sent me was faulty. But Amazon replaced it for me promptly - the new one included a UK plug which was nice since the old one had some weird french one with an adapter, which isn't as good... so in a way, I got a better deal by it being broken!).
It looks good with my iMac since it's black. It doesn't fit in as well as the Mighty Mouse did but it certainly doesn't stick out like a sore thumb.
There is nothing but praise that I can give to this mouse in a Mac - particularly Leopard - environment (I don't think it would work as well in Windows since there isn't any expose or spaces to control).
The scroll wheel is great and the whole thing is literally software customizable to some extent. The buttons can be used for ANY key or key command (So, for example, the two buttons on the side could be used to copy and paste, or type "l" and "o" so that you can write lol without needing to touch your keyboard (although that's pretty sad ;P) or - what I've done - control spaces, backwards and forwards)
It's a REALLY nice mouse and very powerful. You can set the buttons to do different things in different apps which is REALLY nice. Especially for things like Photoshop where you might use two tools a lot.
It's also wireless which is nice, and the best thing is that it's rechargeable, meaning you don't have to spend loads on batteries! Just plug it in and it charges. The battery lasts a long time, too. Mine has currently not been charged for four days and it's only on 2 out of three bars - which is much longer than you get with standard AA batteries like in the Mighty Mouse. Plus, the indicator is very subtle. It's hidden under the glassy bit (Although it's plastic, but it looks like the iMac glass) and only shows up for a second or two (fades in and out) when you move the mouse after it being stationary for a while (The laser goes to sleep when you don't move the mouse as to save power).
All-in-all, if you're going to buy any non-throw-in mouse, I honestly recommend the Logitech MX Revolution to anyone. Scrolls like a dream, feels like a dream but the thing is, it's real!
P.S. A Bluetooth one recently hit the FCC (Which I'm kind of annoyed about! haha) so I would wait for that one if you're going to go for the MX Revolution - it's best to save your USB ports for other things other than dongles, lol.
