I have the Logitech-built, M$ mouse, available
HERE at Newegg. I use it for gaming, surfing, and for just general computing. the thumb ball takes about a week to get used to, with some stretching of the thumb required, as it can be tiresome after three hours of Counter-Strike.
I highly recommend it. I just flick my thumb and it sets the ball rolling...perfect for whipping my CS character around quickly or moving the cursor from one section of the screen to another quickly.
the mouse itself sits stationary on the desk, while the ball is read by an optical sensor.
I've had mine for 3 years, no problems. it is a ps/2 mouse, but comes with a USB adaptor plug, which fits right on the cord. the color of the mouse is black.
~Branson
*edit: I'm a tall guy...6'2" and consequently my hands are big. this mouse is one of the largest i've seen, and is ergonomic as well. I really got tired of using pint-sized mice...my hand would cramp up really fast! *end of edit