I haven´t tried this myself yet, but I thought I should tell you about it. I just came across a text ad exchange. This is probably a lot like regular banner exchanges, but instead of banners you display text ads. I am just guessing, but I think it´s a fairly good guess.
You sign up for a free account, you write a text ad for your site or your business. Then you place a code on your site. Everytime this code, the text ads on your site, is displayed to other people, your text ad will be displayed.
You can read more and join at: http://www.freeadvertisingexchange.biz/