I use the Kensington MouseInABox Pro Optical, which has two main buttons, two more buttons on the sides, and a clickable scroll wheel. It is the best setup I have ever seen in a mouse. I set the side buttons for Back and Forwards in Chimera and the Finder, and the main buttons just like normal left and right buttons, and it works like a charm. The only problem with the mouse is it was designed to be PC compatable as well, so it has a really long cord, which gets in the way on a small desk. Other than that, I would never go back to a one button mouse. On that note, I would hate to see Apple give up the one button mouse. I think that is the best idea they ever had, and if I had to learn to use a computer on a two or three button mouse, it would have been a lot harder to learn. Let the other companies make the extra button mice for those who need that, and keep simplicity and functionality at the core of their systems.
JW