Cut the cord with Logitech V320 wireless mouse, $10 shipped (after rebate)
If you don't mind waiting on a rebate, Buy.com has a sweet deal on a cordless mouse--with free shipping to boot.
For notebook users, a cordless mouse is essential gear. If your notebook has Bluetooth, by all means go for a Bluetooth mouse. If not, you can't go wrong with the Logitech V320, which Buy.com has on sale for $10 shipped (after a $15 mail-in rebate). Sign up for Google Checkout and the price drops to zero (after a $10 instant rebate).
The V320 relies on a USB dongle for 2.4GHz wireless communication with the notebook, which is a bit of a hassle. But at least you don't have to worry about losing it: The dongle tucks into the mouse's underbelly when not in use.
Other than that, it's a pretty basic three-button optical wheel mouse. It runs on a pair of AAA batteries, which Logitech says should last you about six months (provided you remember to turn the little guy off). The rebate deal expires June 18, so you've got time.