Any vehicle at all, from ones that have a real life counterpart like the batmobile or one of the bond cars, to something completely wild and out there, like a banshee, x-wing, or, my personal choice, with appropriate music;
MUHAHAHAHA! I GOT FLU SHOTS NOW, BIATCH!
What? No, not thunderchild. Although if I ever get a boat, I am going to call it that.
What's more badass than your very own three legged, steel tentacled, heat ray equipped, martian killing machine? Not much, people. Not much.
EDIT: Okay, if you say TARDIS, you also have to say something else. C'mon. That's cheating a little. That's being the guy who says he'll ask the genie for more wishes. Don't be that guy. Robin Williams doesn't like that guy.
EDIT 2: Spacecraft DO count. Basically anything that moves you around at a faster pace than walking or moves you through somewhere that you normally couldn't go on your own, like space.