Have you done the bone-headed thing I did recently? I erased a memory card in my camera, and then realized I hadn't transferred the latest photos to my computer. Fortunately, they're easy to recover as I write about in an article at TidBITS: Recover Erased Photos from a Memory Card (2009-06-03).
Although the article's focus is recovering still images, the same tools can recover video, too, which is especially helpful now that more cameras are recording directly to SD cards.
I look at four programs that can get the job done, each with their pluses and minuses: Data Rescue II, Klix, Photo Recovery for Mac, and Image Rescue.