The best thing to do is not let them get corroded. If they're only slightly corroded, I use Collinite insulator wax. You basically rub it on with a fairly thick coating (like waxing a car), let it dry and then wipe it off. I usually do it twice, and drop them every two months and wax them. If this doesn't do the trick, lightly polish them with Collinite metal wax. Rub it on until you feel less resistance, then wipe it off while it is still wet, Do about a 1' section at a time. After, follow with Insulator wax.
I haven't used Collinite, but I've used Woody Wax on a tower. It's effective at removing very light oxidation, but once corrosion sets in, I don't know a solution. Bronze wool can be helpful to knock off light corrosion, but be careful not to scrub off the anodizing. If the rigger's aren't anodized, you can bring them back with most any metal polish and elbow grease.
Woodywax and ruppguard are both ok, but do not last more then a few weeks. (They don't use Ruppguard on Mickey Rupp's own sportfish) The Collinite adhears to it like car wax and will protect and last 2 months........Collinite insulator wax is also the product of choice for most of the sportfish guys on aluminum towers as well........
Capt J's advice is spot on regarding the metal wax and insulator wax, and it's exactly what I do on my boat- a 65 Donzi.