What do you think about sites who specialize in allowing people to exchange ads for free, on the premise that each pageload on the code they give you, (which has ads from other people being displayed randomly per pageload), gives you credits to allow you to advertise your own ad in that same very system? Example: a 1 view for 1 view exchange. You, or a user on your site views the ad code once, you gain one credit to allow your ad to be seen, and whoever ad was just shown looses that credit.