ManyCam is a freeware program which lets you play around with your webcam for fun and giggles. You can add effects, different cool backgrounds, tweak the image in real time and generally spice up your boring webcam life.

The other cool trick is the ability to make your webcam useable with more than one application simultaneously (for instance different video chat programs), which is something you generally cannot do with Windows. You can also add your own home grown effects (such as an exotic dynamic background video) to your webcam chat. Nothing serious here, just a bit of fun, think IncrediMail for webcam video.