Tried selling private ads? Or CPA, sell affiliated products throughout your posts. e.g. cds, dvds, music downloads. Lots of affiliate programs offer those types of offers.
Bribery With CPA give them something if they submit to get something else from someone else then the conversion rate could be quite high!
It will mostly depend on how targeted is your traffic. Do you think your traffic is targeted enought to run CPA offers, or to build a targeted e-mail list? If yes go for it! If not it's always better to run some general PPC income with Adsense. See if the keywords that are used on the SE for find your site are targeted to a specific keyword or are spread out for multiple keywords you were not thinking in ranking for in the first place.
