http://forums.digitalpoint.com

It works like this

After you have made more than 50 posts in this forum, you will earn a portion of the revenue from the Adsense ads shown on the forum. Some members of the forum earn up to US$50 a month by posting and answering questions and comments

You will need to go to the Edit Options area of your user control panel. Within there, you will find an option to enter your AdSense client ID (this starts with pub- and is within the HTML Google generates for you in your account). You can optionally specify a Channel if you wish as well.
Once you have a Google AdSense client ID on your account and you have made more than 50 posts to the forum, any thread you participate in has a chance to show ads that credit your AdSense account.

Its a very good legal adsense revenue sharing site. Give it a try