I know three of them because I've bought from them many times.
John Snow (the best in price and customer service, free updates)
Val1312 (the most expensive in the world, but effective. He charges you every time the indicator is updated. He sells multi-PC and single-machine options.)
Rohit (He charges for everything too. He tries to take full advantage of your ignorance, for example, with the Ninza indicators that come out all the time. He only sells them for individual machines.)