Ever wondered how you'd look in an elf hat, green tunic, and striped pants doing a crazy dance? No?? For some extreme holiday silliness, I recommend Elf Yourself. It's not a game, but it's festive and has great potential for amusement (and embarrassment). The principle is simple: find a photo of yourself (or you partner, boss, enemy, etc); select the facial area in the photo (there is a neat web-based tool to help you scale and rotate your chosen shot) and submit the result. You even get an option to record a voice message to go with it (although disappointingly, this is through a phone line rather than via your PC).
Release your inner elf!