If you've been waiting to learn more about how the Reapers fit into the Mass Effect universe, you only need to wait a couple more weeks. The Leviathan DLC for Mass Effect 3 is coming out on August 28.
A post on the BioWare Blog confirmed the date for PlayStation 3, Xbox 360 and PC. The DLC is expected to focus on the a rogue Reaper named Leviathan. New star systems will be opened and new weapons will be available, and playing through the content could open new dialogue options during the Extended Cut ending of the game.
The new content will cost $10 or 800 MS points.