Remember my front door with all of it's mismatched hardware?
I did some research and learned that you can use lemon juice, vinegar, or even ketchup to remove the oxidization from brass that makes it dark brown. So I decided to try it in an attempt to save ourselves the $500 or so it will cost to replace it. I started with ketchup and squirted a big glob of it on the thumb piece and let it sit there for about an hour. Lo and behold, it was indeed lighter!
So I progressed. This time with an aggressive solution of salt and vinegar.
I took another tactic which was to make paste of equal parts salt, vinegar, and flour and applied the mixture all over the handle. After leaving it on for about 8 hours, I had much better results.
I threw in the towel and told Chris I was going to start shopping for a new handle. So he started taking the screws out. And guess what? It's stuck. That thing is painted on, glued on, adhered to the door with magical powers.
But that's his problem :)
Update 9/1/12: I tried Rub-n-Buff as so many commenters suggested on the handle set and mailbox slot. They both look better, but still not as good as a new set would look. So eventually we'll replace the hardware. Thanks for the suggestions, Rub n Buff is definitely a good interim solution!