I spend a lot of time with my mouse, and this topic is one I've myself spent quite a bit of time pondering. I finally settled on this model, Logitech MX 518, which unfortunately you can't get any longer from most retailers but are available on ebay and third party on amazon. Be careful with ebay mice though. I made the mistake of ordering one that was listed as "gently" used, I don't want to begin to think what was caked between the buttons. The mouse is wired, which I prefer over wireless since I know it won't get away. It also has a nice weight to it and glides effortlessly over the mousepad.
http://www.amazon.com/Logitech-Performance-Optical-Gaming-Mouse/dp/B0007Z1M50
