GunListings.org is a craigslist style website to trade guns, ammo and other shooting gear. Zach Terhark, a 20 year old college student from Iowa and owner of GunListings, says:

Last year I was browsing craigslist.org and I thought I would search for a shotgun because I was in the market for a new one. I then realized that craigslist bans guns. I then go to google to search for a craigslist dedicated to guns, and there were none to be found. At that moment I was determined to make a website where people could buy and sell guns to others in their community for free.

It looks quite useful.