let me second the MX518. Great, great mouse that I've been using for a year and a half now. All of the buttons can be used for spaces/exposé/dashboard, as well as left and right click. And if you use steermouse (which I do) you can also set the buttons to do whatever else you want, like forward/back, page up/down, and pretty much anything else you can think of.
It's a great, accurate (1600 dpi, or 1800 on the revised version), and comfortable mouse. Logitech has some great choices. My gf has a vx revolution, and that's a great wireless (though not bluetooth) option.