On my last bike, with aluminum rear wheel, I used 'Flitz'. By the end of the first season my buddies were asking if I had the wheel chromed. I would buy the packs of circular wax applicators like the ones in the paste wax cans and use them to apply the Flitz, then use pieces of old bath towels to polish if off.
Works like a charm. Also keeps the water spots from becoming permenant marks on the aluminum.