I think Empty Spaces and the Weird Al song are the only intentional ones in there.
I'm surprised nobody has mentioned Aphex Twin (unless somebody did mention it after the 2 or 3 replies I read) who scanned images of his face to digitally generate some of his music, and as a result his face can be seen by playing certain tracks through special audio software.
Link here: http://www.wired.com/news/culture/0,1284,52426,00.html