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Forum Moderators: phranque
The best way to do it, is still word of mouth and via contacting webmasters. It takes leg work and it takes work to make contacts. Those contacts will pay off in spades down the road. Something as simple as an a well written low key email is often enough - short sweet and too the point of being terse - webmasters are all suffering email overload pains at this point.
A banner network by its very nature is a viral thing. I don't know of any importan banner exchange that has been built by advertising alone. It is all word of mouth.