Lowes has metal polishes. There are five different ones, each for a different part of the process. I believe that I used #2 and #5 for my kegs. If you want to support the guy who started the polishing movement on HBT try this website.
+1000 on the "polishing your keg" is more than a clever euphemism thread. I just spent the afternoon "polishing my keg" and building my immersion chiller. (Downed a few Legend Brown Ales in the process) The keg looks awesome. Have to pick up some threaded end fittings for the chiller tomorrow. Pics after installing my spigot from bargainfittings.com.