Florida has around 120, http://www3.hsmv.state.fl.us/Intranet/dmv/specialtytags/specialindex.cfm
Some of the more interesting themes include "Imagine", "Fish Florida", "Aquaculture", "LargeMoth Bass" (this seems to be very popular, I have seen it often. We have a "Challenger" plate as well.
However, I think a year back or so we passed a bill to limit what could be turned into a commerative/funraising/etc. design for a plate, because we were going on overload with choices. I never looked into it, but remeber hearing it somewhere.