In my experience none, I even tried doing my own but still had little sucess.
It has been my experience that either the sites have your banner on a lot of unrelated sites or that you don't get any clicks. Another thing that I had problems with was that the exchanges would not release a list of the sites in the network, so you had no idea where your sites were being posted.
If you do find a good exchange I would like to know about it. I have a site that I would like to get more traffic to, but since I don't earn revenue from it at all I can't afford AdWords or the like
i have been looking for a while and have not found one yet! They all do not offer the best deal! i am trying to find one that fair and does not put ads on about its self all the time!
