A few years ago, I saw a t-shirt that spelled "WWU Chemistry" in the style of a periodic table. So, I decided to throw together a DHTML program to spell an arbitrary phrase this way. Today, I cleaned up the code a bit and added sample phrases. The algorithm prefers two-letter combinations to one letter. Unfortunately, a lot of common letters can't be done exactly, so I had to be a bit creative.
Here's the link. 2012 Edit: In 2005, only IE could flip text, now Firefox can too, so I'm using css3-style rotation.