51: Ya, we are running alum. driveshafts.
I wouldn't suggest aluminum driveshaft AND cups. The reason behind the alum. driveshaft is that it is sometimes much truer than the composite. Running the alum cups is a bad idea altogether, whether you are running the stock shaft or aftermarket. If you do, you risk busting out gears instead of the cups, especially if you run the alum. shaft.
Brands. Well, we run the IRS shaft. I know Hardcore makes one, and I know I've seen 2 or 3 other companies that make alum, titanium and magnesium shafts. Stick with alum. It's cheaper and just as durable.
Just remember to ALWAYS run the little red rubber o-ring in ONE of the drive cups.