Over 2 years ago I won a free Logitech Cordless Duo. They were both awesome, although I doubt I would have paid $80 at the time for both.
Since then the mouse, which had really bad battery life and the paint coating coming off, was replaced with a Microsoft Wireless Intellimouse Explorer 2.0 (I got it at Staples last december for $7 on sale). I like this mouse a lot more because it gets much better battery life (I've left the mouse on (no on/off switch) for almost 6 months straight and Im still on the same set of batteries) and it has the 4 direction scroll wheel. Its also a bit more comfortable to handle..
The only bad thing is I have 2 recievers now since the Microsoft mouse isn't compatible with the Logitech reciever, but I still need the logitech reciever for the keyboard, which is still going good and I have no problems with it.