NOTE: Rick Findley has an ongoing project to create a DIY surfactant base and is having some good success. Read about it at RAD Recipe which also contains notes about surfactants tried and failed. People frequently ask if there is a way to make their own surfactant base for bubble juice rather than relying on commercial detergents like Dawn and Fairy.
The answer is: it is probably possible, but it is not a trivial task. Many have chased this dragon for years and given up. Unfortunately, none have been willing to share information about their successes or failures. So, each new experimenter has started from scratch.
We know the important ingredients (the Dawn Pro ingredient list can be found Manual Pot and Pan here) but apparently very small differences in amounts make a large difference as do the particular ingredient sources.
Of the many that I have known who have tried to come up with a reliable base, only one person: a professional chemist has announced having come up with anything usable. He announced on SBF, the Soap Bubble Fanciers Yahoo Group that he had come up with a mix that performed almost as well as Dawn/Fairy after several years of experimentation. Since he was (is?) developing this as a potential product, he would share no details other than to say that it was based on what he gleaned from the patents and that it still required enormous amounts of experimentation to come up with something that worked well -- but still not at the level of the commercial product.
There is a guy in China working on his own base who says that he will share it on the wiki, but I have no idea if that will actually happen. I hope that he will come through!
For ingredients used in various detergents see: Detergent Ingredients.
Nov. 2016: Rick Findley has posted a DIY surfactant base: RAD_Recipe