I'm sure there are mice out there with thumb buttons, but there are also trackballs with that feature, and any number of game controllers can be programmed to use a button comfortably with the thumb.
Logitech gets high marks from many, and this group now includes me. There's a thread somewhere where quite a few members swear by Logitech mice. I've recently started using a Logitech Attack 3 joystick game controller, and love it. I was using a generic game controller, but it felt kind of "loose" in response time, the latency seemed slow and inconsistent. But the Logitech has a tighter feel, and responds quicker. (Although the software sucked. If you get a Logitech game controller, use the free program Xpadder to set it up.)