Metal Rescue is an environmentally safe product that literally dissolves the rust away. You just drop in the rusted part, let it soak for a period of time (the worse the rust, the longer you soak it), and presto, the rust is gone.
Another benefit is that it doesn't remove any of the metal. I needed to get the rust off of my old Triumph rotors and didn't want to damage the finish. As you can see in these before and after photos, Metal Rescue just made all the rust go away.