I like the three button UniMouse even more. The driver can't be configured, which also means nobody can change your settings. Instead, you have several preconfigured drivers to choose from. Drop my favorite into your System Folder and the left button clicks, the small center button double clicks, and the right button pulls up the contextual menu. Contour has won several awards, including one for the most ergonomic mouse.
Some models even come in different sizes for different hands.
Based on a day with the UniMouse, I'm sold. The UniMouse comes in colors to match all the new iMacs, as well as the G3 Pro. I hope Contour will take a stab at. And if you're tired of grabbing that Apple puck-mouse the wrong way, consider it a great way to reduce mouse frustration. UniMouse Overdrive lets you program a button for active scrolling.