There's a product called "Spotless Stainless" that was recommended by Maine Sail in one of his posts a while back. I bought it at the beginning of this year and didn't get around to using it until yesterday. The images below show the before and after for the same fitting (taken at different times). The product works as advertised. You brush it on, let sit for 1/2 hour, and rinse it off. The heaviest oxidation needed a little help from a scotch-brite pad.

I would recommend this product -- you get a good result with not a lot of work, and it passivates the stainless at the same time.