The Logitech trackball shown above is a fine mouse. Keep a lint free cloth handy for cleaning and don't ever use any solvents (windex, 409) on it. If you must use something, use handsoap. Once the slick coating is gone from the ball it will become difficult to make small movements. You can get replacement balls from Logitech when that occurs.

I always found these mice to be very hard on the thumb. Instead of moving your whole forearm for movement you are bombing your thumb with all the movement tasks. If you do really long gaming sessions you will feel it. In fact my thumb starting hurting just thinking about gaming with the track ball. I use a standard gaming mouse for boxing and mouse steer alot with it. Mouse steering is a bitch with a trackball.

I have used Logitech trackball mice since '94. My first mouse from them clipped on the side of the laptop. Invaluable when you are trying to do things on a pc in the engine room of nuclear sub where there are very few flat surfaces and oil mist gets on everything.