If it's fairly benign...elbow grease and a product like Napa's Chrome polish or Maguire's Gold Class Metal Restoror or Mother's Chrome/mag Wheel polish. If you get something too abrasive, it'll scratch the heck out of it. Napa's polish is as abrasive as I'd use. That is, a rubbing compound might be too much.
If it's really bad, get an attachment for your RotoZip/Dremmel/drill with a felt nubbie and go to it with that and some good compound. Go to Griotsgarage.com for an idea of those. I'm sure the stuff they have is good, but waaaay too expensive. Remember, if it's pitted really badly the chrome will be gone...I've used #0000 steel wool directly on the rusty areas, but try to avoid the existing chrome - even if it doesn't matter what it looks like, then treated with a good polish. (most of the time, it's white...blends in with the chrome )
mine were rusted up pretty good, got 90% of it off in short order just using some turtle wax chrome polish I had lying around. The chrome on the stock wheels is pretty high quality, it's amazing how well they'll clean up.
6-pack of Coca cola and some steel wool work nicely on chrome wheels and don't leave any scratches. Pour the coke on the rust and rub away. Just don't drink the used coke.
I have cleaned up two sets of Factory 60 wheels and a quick and easy way to do so is to use a brillo pad and som e water, this causes no surface problems while also removing rust at a fairly easy rate. If you choose follow this with a chrome polish as mentioned but i did not find it necessary.