I miss my third mouse button on virtually any mouse these days. I fear that my last Logitech MouseMan is about to die. The only appropriate mouse I can find these days is Sun's Crossbow mouse. At least it comes in a USB format -- I may get one of those for home use.

And, yes, I know that you can press the scrollwheel for a third button, but I dislike scrollwheels and it's very hard to press -- too small and too much resistance. In reality, I'd probably dislike scrollwheels less if they didn't supplant the middle button.