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Forum Moderators: rogerd
What we did is we have optional paid subscription. Paying members can opt to switch ads on or off. That way, if people really hate the ads, they can take them off there by paying $5 a month. Surprisingly, many of the paying members keep the ads. They say that they'd like to help us a bit more. Also, some of our ads are targeted and they want to see those :D
BTW - I think Fastclick doesn't allow ads on forums. I would suggest checking with them first.
Having a monthly banner sponsor is another idea I have used.
Be very careful here - this is against the Adsense TOS's. I'd do a quick reread just to make sure what you're doing is within them - [google.com...] (incentives to click...)