Adsense is not the best way to bring in revenue. Sure it works but the real money is in private advertising. Ie. Say your website is REI related (example since this is an REI forum). Your best bet once you have the traffic and the stats to back it up is to find direct advertising from companies in that niche. For example, if you look a the top of the BP forum, you will see RealtyTrac, forclosure.com, ext. My guess is these are direct advertisments. (they pay BP directly, using no 3rd party and at a set monthly rate based on page views/page loads/ext.)
You can also step into affilate marketing. If you do not know what that is, basiclly you advertise products from other people and if someone buys the product you get a percentage or a set amount. If this interests you check out Commission Junction, they have affilate programs from all most any niche you can think of.
There are also affilate marking companies, similar to Commission Junction, which sell ad space based on impressions (ie. page loads). However, most of these are popups/popunders that usually annoy visitors.
The best way to go about figuring how/what to advertise on your site is to know your visitors. That way you can choose which type, brand, product, ext. of advertising they will be more likely to click/purchase.
Hopefully this gave you some more ideas for monetizing the site, other than relying solely on adsense.
-Matt