Best stuff you can buy for the chrome exhaust tip or anything metal you want to restore to the original shine is this stuff called, "HEAVY METAL". Car show guys rave about it, and I use it too. You can only find it on the web or at a local big truck parts store. These guys use it on their 18-wheelers and all that chrome/alluminum stuff. There are two versions, heavy duty and fine grade. I use the fine grade stuff on chrome parts and the heavy duty stuff on the exhaust its self. They some times sell it at car show conventions. It's not cheap but works great. The guys on American Chopper also use this stuff on there bikes. Here is the web site.
http://www.heavymetalpolish.com/Products/