Simichrome
I'm surprised no one has mentioned Simichrome. I see mostly knife collectors using it. It seems to be less aggressive than the others and is really easy on the blue. Most good motorcycle shops carry it, as well as most other polishes. We have an Ace hardware store here that carries just about everything. $10 is a good price and it usually sells for $15 for a 1.76 oz. tube. I's very mild/nonabrasive, like a cream. All my knife buddies swear by it, and my gun buddies. I'm sure there's a thread on this forum that gives you the pros and cons. I just finished my Winchester 501 Grand European and it looks great.
I guess I should retract the term nonabrasive. It has been stated on this forum, correctly I think, that all metal polishes are abrasive to some degree, but this stuff is very mild.