Wireless Intellimouse Explorer 2.0 that I've had for a few years...
nearly identical to this one. The battery life averages three months and this is a great gaming mouse. Wireless reception is quite finicky unless I keep the receiver close, but beyond that it works perfectly and tracks without a single issue. It's been such a good gaming mouse I'm looking at the Microsoft Habu to potentially replace it soon...
I also use some basic wireless Microsoft multimedia keyboard, it also works well and the battery life is even better than the mouse. I really really hate the F-lock key though, as it defaults to the function keys disabled after every restart and there's no status LED to indicate if they are enabled or disabled.