My top pick is SR-71, then Concorde and "Concordski" (Tu-144). But I also like the looks of the original Boeing 747 Jumbo Jet. I love the hump, and its overall proportions!
Most airplanes, but design, are beautiful. I think we will eventually see most airplanes ever produced listed here. I think a more manageable thread would have been "What is the ugliest airplane?". There are few out there.