There's a dealer (well, a bunch next to each other) in LA that sells Jaguars, Porsches, Rolls-Royces, Bentleys, Mercs, and Audis. In that order. I saw a Carrera GT in the showroom, surrounded by about 10 Boxsters, next to two Rolls-Royce Phantoms and a Corniche, with two Arnages (T and R) and a bright blue Continental GT. Hell, I didn't even notice the Jags and the rest, I was too busy sitting in that Corniche.
Going up Los Angeles Crest Highway 2 I saw two Viper coupes and a nice Evo, which was definitely worth mentioning.
Florida's great for Porsche watching: they're practically the Toyota of supercars because there's so many there. The rest is vulgar.
Finally, in Waltham, MA there's another uber-dealership that sells Aston Martins, Saleens, Lotuses, Spykers, old Porsches, and little boys' dreams. I've mentioned it before, but it's worth mentioning again.
http://www.astonmartin-lotus.com/