not that i totallly recommend it, but i bought a logitech optical trackball with 4 buttons plus a function for clicking both and i thought i'd hate it after the first five minutes, but it's grown on me to the point that i hate using normal mouses, wired, ball, whatever. I just love being able to use one finger for controlling a pointer across two monitors. saves me a lot of wear and tear on the wrist.
I've also gotten accustomed to it in games like quake/quake3 and its' just being second nature to me.
wiht that said, the microsoft intellimouse above is very good. I lieke the front/back buttons as well.
4-5 buttons min, though
