If clicking multiple buttons is too strenuous an activity, check this mouse out.
The Z Nano Optical Mouse, which bills itself as the "world's tiniest" optical mouse, is, at 1.65 inches by 0.83 inches by 0.69 inches, barely larger than a human finger tip. It plugs into any PC via a USB cable, and instead of right and left click buttons, the user needs only to roll a finger to the left or right instead. And in the case of scrolling, you click buttons on the mouse's side.
The Z Nano has clear plastic casing and is lit by multicolor LEDs on the inside. Under where the finger goes, there's also a place to insert a tiny image to personalize the device.
It costs $60, and is available on FlipAlbum.com.