There are currently 100,000 used video games up for sale on Switchgames.com

"SwitchGames is a game trading site that has ridden the wave of demand for used games. Today, the company says its users are now offering more than 100,000 items for trade on its peer-to-peer game trading community.
The New York company, which was a finalist in the GamesBeat 2009 startup competition, makes it easy to trade games quickly and safely without fear you’ll be ripped off. The company hit its 100,000-item milestone in less than a year, said company founder Jason Crawford.
Overall, used games are a $3 billion business. Much of that is traded through GameStop retail stores. But users don’t get paid very much, while GameStop resells the games for a tidy profit. SwitchGames instead empower users so they can get much better deals."
Source: Venturebeat, 19th January 2010