[rkangel]

One aircraft that I have always assumed existed was the SR-71 replacement. When they retired it the official story was that it was superceded by satellites, but satellites have a level of predictability and trackability that is best complemented by an aircraft. I have always assumed that they had a replacement with capabilities that were once again classified.

That said, I don't think you'd find it at Area 51 given the fact that it would have been in service for a while by now and that Area 51 is more about testing experimental aircraft.