Not many for me. Can only think of DFW but I'm sure there must be a few others.
Excellent question, OP - it'll bug me for the rest of the day now!
I suppose it also depends a bit on definitions. I took the above to mean places where I never left the airport. If I consider places I've been to on business where I've seen precious little more than a hotel, office and airport there'd be quite a long list.