I was wondering what airlines registered in the USA operate a Boeing 747 ?I could only think of 2: United & Northwest Airlines, are there more?-Mike

I think UAL and NWA are the only U.S. flag scheduled passenger airlines that use B747s. There are a bunch of cargo lines that still fly them: Atlas Air, Evergreen, UPS, Kalitta, Polar Air Cargo, TAG charters, Wings Worldwide, Southern. Of course, NASA still has a couple, too.

And don't forget the USAF.YAL-1, VC-25, maybe some more specialties and one-offs we've never heard of.