Mobee Technology Magic Charger
While most Apple users I know like the Magic Trackpad, I still prefer a mouse most days while at my desk. I use Apple's Magic Mouse, which while a few years old, still works really well with OS X's ever-growing collection of gestures.
The Magic Mouse's battery life isn't terribly good, however. The Mobee Technology Magic Charger was designed to change that.
The $40 gadget snaps in to the bottom of the mouse, where the door for the AA batteries is. It sits flush against the bottom of the mouse, so it doesn't feel or look any different than a regular Magic Mouse.
Inside, the Magic Charger has a rechargeable battery. The battery and cover stay juiced up via inductive charging. The mouse simply has to sit on the USB-powered cradle one night a week to keep things running smoothly. Spare battery packs can be had for just $20.