What mouse do you use and why?

I've been using Apple's Mighty Mouse (with cable) for a long time and I love it.
I wouldn't want to miss the tiny 360-degree scrolling ball and the design of the mouse.

However, I have to admit that I haven't used mice with my Mac for months - I'm in love with its glass trackpad. I've always been a mouse user who disliked trackpads, but this one is different. It makes you forget that you own a mouse.

Whenever I'm using a desktop PC or Mac, I'm using a Mighty Mouse, though.