Meguiar's NXT All Metal Polysh or Meguiar's Hot Rims Mag & Aluminum Polish both work extremely well. At a recent session at Meguiar's I cleaned up the exhaust tip of a Honda S2000 with over 100,000 miles on it and the owner says he has no recollection of ever cleaning the exhaust tips. The transformation shown took a whopping 5 minutes. A friend of the owner went back later and spent another few minutes cleaning out the inner portion of the tip with the same product.