One from the "why didn't I think of THAT" department: a fisheye lens from a standard peephole just like in your front door. You can pick up a peephole (sans door) for around $10 at most hardware stores and be shooting cool ultra-wide-angle, amusingly distorted images with your point-and-shoot digicam in the time it takes to simply tape it to your lens. Adding similar capabilities to a fancier DSLR can easily cost 50 times as much. Yay, cheapness!