[berettafan]

I've used very fine grit wet/dry like you get in an auto parts store with some gun oil for slight amounts of surface rust. slow process but works very well. Though once you've got visible pitting it's probably best sent to someone to strip and reblue.

edit: this will of course remove bluing but what's the point in worrying about that if you've got rust? I think not terribly expensive to have a gun reblued by a pro.