[Aron9000]

Rust is the big issue to look for. Look on the lower rockers, the lower edges of the doors, door jambs, fenders(look along the inside edge facing the wheel), trunk(look under the mat), floors, and leading edges of the hood. Another place notorious for rusting is at the base of the rear window.

I'd have the car put on a lift and looked at before you buy it, so you have no suprises.

Other things to look for: worn suspension bushings, tie rod ends, ball joints, shocks, etc. I'd also make sure all the wiring is in good shape and the accesiories function like they should, nothing worse than fixing hack jobs on the wiring or tracing bad grounds.