Price: Apple Magic TrackPad, $69.99; Logitech Wireless Rechargeable Touchpad T650, $79.99
Sitting at your desk all day constantly using your mouse has the potential to do a number of your wrists. To prevent any injuries or inflame a case of carpal tunnel syndrome, a mouse that doesn't require your wrist to move is your best bet.
We recommend giving a trackball like Logitech's Wireless Trackball or Trackman Marble (for the lefties in the world) a try. Even better for prolonged use is a trackpad similar to the ones found on laptops. For Mac users there's the glass-covered Apple Magic Trackpad which is basically the same one found in MacBooks. For PC users, there's the Logitech Touchpad.
Both allow your wrist to stay relatively stationary while giving you a full range of multi-touch gestures found in Mac OS X and Windows 8.