I have used the TK7-Super fuel additive. I liked it because of its reported anit-wear properties by David Vizard, of Motortec Magazine. Jan 2001. Gas mileage may have been up with it too. I recent ran out and my mileage is down.
More info on this site. http://www.bndautomotive.com
Edit: I see there is another recent (2005) article mentioning the QuantumBlue lubricants. It is linked on this page.