Today I saw a late-model Toyota Highlander Hybrid, in black, blast through a downtown Seattle intersection (heading toward the helicopter crash, I'd guess, based on the time and location) with red-and-blues flashing behind the grill and in the rearmost side windows. It actually took me a few seconds to stop mentally cursing the soccer mom running a red light, realize that it was a police vehicle, and get the hell out of the way.
I'd never seen such a thing, although now that I look into it, it looks like some tonier municipalities have adopted the Highlander as a police vehicle:
But the unmarked (or ghost-marked) police vehicles here—from the city cops to the county sheriff to the state patrol to the feds—usually seem to run a very typical range: several Panther platform sedans, American SUVs and vans, newer Chargers, the occasional Prius for some around-town duties (the state motor pool has a lot of them for state agencies to use), etc. The Panthers and SUVs come in several colors for maximum stealthiness, although every unmarked Panther I've ever seen has cop steelies, which is a bit of a giveaway.
So: what's the most unusual unmarked police vehicle you've run into (hopefully not literally)?