True, using Google Adsense would be against TOS, but you could curtail your own ad engine. For example, you can create an Amazon affiliate account and display books that match the keywords in your small ad space. (anyone who clicks on a book and buys will earn you money for the sale) Everything related to affiliation (provided that your keywords lend themselves to this kind) will work. Consult with TOS affiliates, but since they tend to pay on sales, I donโt see a problem.
In the late 90s, Eudora did something similar, and Microsoft is now doing the same with their "Live" products. But I donโt know, someone is doing the content delivery side ... (the opportunity is there!)
Unfortunately, other ad programs received very poor rap. (e.g. Cydoor, Claria)
My advice would be to create an application with the ability to display ads and a basic controller that captures the xml file of available ads from your site. Initially, your xml file could have nothing but "how is this application"? Donate'-ad, but as soon as you have a lot of users and you see that your application will use an honest bit, then itโs worth trying to sell the advertising space in your application.
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