I am involved in a cool project that just launched - FleamarkAd.com. FleamarkAd is a classified Ads platform that completely integrates with Facebook. To signup and post ads you only need a Facebook account. Through your settings you have the option to share the Ad to only certain friends on Facebook, to a certain Facebook group or as well to everybody on the Internet.
contest to win one of two iPhone 5 for people that join or like the app.
Additionally there is a cool feature that allows you to print your ads so that you can put them up on boards in your School etc.