A trick that I learned when I worked at a body shop on old chrome bumpers.
If you got some heavy rust, use steel wool.Lightly though.
Also comes in handy for old chrome rims that you want to unload quickly without putting a lot of time and effort into.

I've used the Never Dull (or however they spell it on the can), and like Chris said, it takes a lot of elbow grease, but it does work. I used to use it on the chrome/aluminum exhaust tips on my old 99 grandam gt whenever they would get tarnished.

 

I just saw it at amazon.com or gs-27.com for $8 or $9. I assume this stuff works pretty well? I've got a horrid scratch on the hood thatI'm pretty sure ti won't work on, but I also have some swirl marks from the dealership's car wash I think that I'm thinking of trying this on.