One of the things that put late night talk show host Conan O'Brien on the map was a segment where he'd take a picture of someone's face and superimpose another person's talking mouth over it. It was creepy, it was awkward, and now you can do it too with a service called Mashface.
To make your own horrific creation, you pick from one of the ready-made photos of celebrities and politicians. For now you're limited to just these photos, but I'm assuming users will be able to upload and mark up their own photos in the future. Once you've found the right shot, you simply record up to a minute of audio and video from your Webcam, and it can be placed in layers on top of the photo. This includes things like your eyes and mouth, although depending on the photo, you can use the tool to mimic hand gestures too.
The tool lets you tweak both the size and shape of your recording, along with the color tone, so you can try to match your skin with the person you've chosen. This works pretty well, but getting a perfect match is tough.
The creation I made only took a few minutes to put together. The final product was processed and pushed live just a few seconds after hitting the publish button. The service attaches a little promotion at the end of your clip, but otherwise it's completely free and the videos can be placed elsewhere like what I've done below.