So you know some of those old Grateful Dead logos, that say the name of the band in both directions. (upside down, et el.) This guy, John Langdon, has been creating his own for quite some time, and even did the Dan Brown Angels & Demons logo design. I spent quite a bit of time perusing his site. 
...oooh just found a link to another designer that does ambigrams. Robert Petrick wiki
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