Can't believe no one's mentioned this yet: the Batwing. I've seen several versions of this vehicle, and not a single one looks like it could ever get off a runway, let alone dodge among Gotham's skyscrapers. They all look cool, though.
Honorable mention goes to the Klingon bird of prey, though it's another really cool-looking ship. Ditto for enormous Star Destroyers cruising idly through some planet's atmosphere like old-fashioned (and light, aerodynamic) Zeppelins.