logitech mouseman optical.  it had problems with the wood surface of my desk (had some parallel grain, when it went over the second it thought it was back on the first and would skip) but when put on a mousepad it works just fine.  haven't had any problems with it tracking when i picked it up, either.  and the feel of gliding is so much better than the ball.  i still have my old mouseman wheel plugged in, just in case i ever play a twitch game the optical can't handle.