I have the Logitech Cordless Desktop MX. The mouse uses the fast MX engine so its one of the few cordless mice that are suitable for playing games without lag. The batteries only last a few days in the mouse, however they are rechargable and the receiver unit acts as a recharge docking station, so I just drop the mouse in it every few days and its back on top!
Can't recommend it highly enough. I tried the M$ ones for a few days, but there is noticeable lag, and it lacks a recharge station. The Logitech ones are perhaps more expensive, but I have to say I am totally satisfied with mine!
