Read around this particular forum, there is a "definitive" TCW-3 thread, with all kinds of ratio/dosage recommendations
But the most popular seems to be 1 oz. of TCW-3 per 5 gallons of fuel....preferably added BEFORE pumping, so you can get it down the throat/filler tube of your gas tank
The gas'll help wash it down into the tank
Other than TCW-3?
There's Marvel Mystery Oil
Lucas is "the original" (in my book - being that it being the first product I ever seen that mentioned the term "upper cylinder lubrication" on the packaging....) UCL.....BUT, I would NOT consider it a fuel system cleaner.....it's been stated here previously it doesn't contain much "detergency" at all.....compared to say TCW-3, MMO, etc....
Seafoam is another good one, depending on who you ask, you'll find haters, and lovers of the product; according to the public MSDS sheets available, it's primarily Naptha (think lighter fluid?), IPA (another words, 100% rubbing alcohol....the stuff in your medicine cabinet is likely only 93% alcohol, 7% WATER...), and a light based "oil"...
Seems STP is getting "back in the game" per se too now! They got a new "Multipurpose Additive" out, advertised on their site, and facebook profile, which is gonna be the supposed Seafoam competition....and I don't know.....it could beat it out, if it performs as good....the STP is $2 cheaper in my neck of the woods ($6 and some change, Seafoam is $8 and some change....) - and the whole "jab" at Seafoam seems to be that the STP product does NOT or will NOT contain "alcohol" which is supposidely bad for fuel tanks, engines, etc....can cause combusion problems, allegedly....but I dunno, I've had no problems with Seafoam the many times I've used it!