Like people, like car portraits - long lenses.

Tip I remembered from one of the N-Photo apprentice under-a-pro-wing sections on cars - you want to shoot cars with at least a 105 or a slightly longer lens to avoid distorting the shape. Seems like common sense, but realistically 90% of the people get their wide angles out to shoot cars at shows, events, etc from what I've noticed. I know I slack on this too when I'm at car meets, but there's also seldom all the room in the world to stand back properly.