I've obtained a pretty nice brushed looking finish on aluminum using a pneumatic body file like this:
http://www.harborfreight.com/cpi/cta...emnumber=91773
I used a roll of this:
http://www.wttool.com/product-exec/p..._Sanding_Rolls
The finish left was pretty nice. The down side is that the body file is pretty loud, and my little old air compressor couldn't keep up very long. If you're work bench is of normal height, you'll end up with a black belly, too.