Brad Honeycutt, a fellow Spartan (he graduated 1996 a couple of years before I started here at Michigan State) is fascinated by optical illusions. He has completed a couple of books on optical illusions the first of which will be coming out in July. Scott Kim, one of my favorite ambigrammists, contributed a foreward and it includes work by Scott and John Langdon (he of Angels and Demons fame).
Brad also runs an optical illusion blog at http://www.anopticalillusion.com and recently featured one of my ambigrams.
This design is one of my favorites… do check it out on Brad’s website, he includes the ambigram and a short note from me regarding how it came to be.