If
price is your concern, then there is another
Microsoft IntelliMouse, except that it's
white, not
silver, and there are just as many buttons, but they only one is activated by the
thumb, the other is a
pinky based
button. Yes, it's an
optical mouse.
This cost me $15 (USD) less than the silver one. It's got the scroll wheel too, which is vital for me, because I scroll up and down through things a lot.
The only thing I've noticed about being optical is that I have to clean the camera off occasionally (once in 3 months), and it won't work on my guitar (too shiny, I suppose).