Very tough call for me. Probably have to go with a 1967 Ferrari 275 GTO 4 cam. An extremely close second would be the new Ferrari 599 GTB.
There are a myriad of American muscle and race cars that top my list as well. A 1966 Ford 427 Cobra A/C is right there with the 599 for me. My favorite variants of the Mustang, Camaro, GTO and 'Cuda are not far behind. I could also live with an Aston Martin One-77 or DB9, an SL65 AMG, a BMW M5 oe Audi R8. Judas, I love cars - be right back....