Both Gamestop and Amazon are making a bid for your used games with tantalizing promotions. For Gamestop's part, the used-game reseller has been running a tiered trade-in offer. Trade in at least 2 games and get 10 percent extra credit. That number doubles to 20 percent if trading in at least 4 games, and doubles once more to 40 percent if trading in at least 6 games. Naturally, the trade-ins must be in full working order and the offer is good towards games only.

Amazon, on the other hand, has begun a tiered offer of its own. Send the company two used titles and receive an additional $10 off select new releases, or send the company four games to receive $20 off. These credits are in addition to the Amazon.com Gift Card sellers receive when trading in used games. See here for a list of eligible new releases, which include titles like Halo Wars Limited, Resident Evil 5, MLB 09, Street Fighter IV, and a whole bunch more.

Amazon launched its trade-in store earlier this month with 1,500 eligible titles. The company foots the shipping bill when you send in your used games, then issues Amazon credit in the form of a Gift Card, which can be used anywhere on Amazon.com. A quick glance of eligible titles reveals slightly better trade-in pricing than Gamestop in many cases.

Gamestop's promotion runs until April 5, 2009 and Amazon's until April 12, 2009.