64 GTO and 71-72 GTO Judge for American although I have to admit I really like the 426 Hemi Daytona's with the huge rear wings. I have always liked f-bodies and 60s mustangs, and the shape of a Cobra is a classic.
Can't forget the Brits in all this either, an MGB or C with a UZFE in it (very tight squeeze I think) would have to be close to the ultimate sleeper, no one would think it could do anything just by looking at the exterior of the car.