Try scotchbrite rub in one direction back and forth. Look at some of Exile choppers custom bikes that is how they get a cool brushed aluminun look throughout thier builds. Another cool thing I have seen then do is ceramic coat (hpc) frames and then hit then with scotchbrite the whole frame looks like its stainless steel. Its a nice alternative to the shiney chrome.
Pushrod is on the right track with the coatings. I've spent some time with the place that does my coatings, and they've shown me quite a few different shades of flat, high temp coatings, including a few that look exactly like raw aluminum.