I've noticed a trend of making a mosaic of a famous person (often as a character portrayed by that actor), and then getting them to autograph the mosaic. I've previously mentioned Josh Wedin's Pinky and the Brain and Dave Shaddix's Spock and now with a matching Kirk (check out the signing in action!) and McCoy (which will, of course, remain autographless).
Earlier this spring, Dave Ware got in on the action, making a mosaic of the character Jayne (as played by Adam Baldwin) from the TV series Firefly. Here's a photo of Dave, Adam, and the mosaic: