Reaching what is probably the final frontier of novelty last-gen MacBook mods, Macmods member EdsJunk has put a full-function color LCD inside the Apple logo and hooked it up as a secondary display.
His post is minimal, so we don't know how he did it, what kind of screen he used or how much it cost. We do know, however, that running the an iTunes visualizer or iSight feed in the apple is categorically awesome. UPDATE: Oh my, it's on eBay. [MacMod —Thanks, Chris!]