Depending on the condition of the paint and clear coat a buffing compound could work. I've always been a big fan of 3m Microfinish. It isn't to harsh but it still can get the job done. Just be sure to use a polishing glaze afterwards. I once used it on my friends faded red Probe and it made a huge difference.
i have the same problem and i used this polishing compound from turtle wax its in a white container at any store for like $2 and holy crap it made a differance, i also used one of those spunges for dish washing the one with a soft side and the scrubby side, i used the scrubby side and it worked perfect.