I agree with the vinegar. We usually just fill a Ziploc bag with some vinegar, stick the faucet inside the Ziploc bag and put a rubberband around the faucet and bag and let sit for awhile. It comes clean every time without any scrubbing. (04/05/2009)
Vinegar is an acid, so you'll want to test a drop on an inconspicuous part of the faucet before you do the whole thing.
Based on a review in Family Handyman I tried Bring It On Cleaner on my horribly stained faucets. I had to leave it on for a few minutes, but I'm satisfied with the results.
I was able to get a free sample at www.bringitoncleaner.com. (04/07/2009)