Of all things, an Aston Martin Rapide S - it was behind me, so I could tell Aston immediately, but I didn't twig it as the Rapide until I turned and it didn't. Never even seen one of these at C&C.

Also saw a very tastefully modded Legacy Spec B out on I-66 - not nearly as unicorn-y, but you don't see a whole lot of them either.