Freak Show is a crazy fun house mirror program-- a deluxe version of Apple Photo Booth.
The free version has all the effects of Photo Booth and runs on computers that can't run Photo Booth. The paid version adds nine incredibly cool effects, the ability to create your own Freak Show Quicktime movies, and a Freaky full-screen mode.
You don't have to have an iSight to run Freak Show. Firewire DV cameras give great results. You can also use most webcams, and iSight, of course.
Unlike Photo Booth, Freak Show doesn't need Quartz Extreme and runs on any Mac that runs Tiger.