Here's another entry in the "not super useful, but definitely super fun" category: Ice Cream Sandwich gives you a few nifty effects to employ when you're taking a video. Add a background to make it look like you're in space or standing in front of a sunset. Or give yourself huge eyes, a swollen nose, or a scrunched head. The effects all work surprisingly well – they're a good way to make a goofy video for a friend. Just select the options menu from the camera app and you'll find the effects nestled in there with other controls like color and exposure.
If you're not on Ice Cream Sandwich, check out the free Videocam Illusion app – it'll give you a lot of the same features.