I recently got the Logitech Mousman Optical, and I have to say it rules. I had the Logitech MouseMan+ (the curvy one), and it was terrific as well. The new mouse is incredibly smooth, and I'll never have to worry about the rollers gunking up ever again!

The new mouse also has four buttons, which I've gotten quite used to. Now, if I could only get the fourth button to work under linux as something useful.