Halo 4
Not much is known about this upcoming project. Halo 4 is the first Halo game announced in a three series called "The Reclaimer Trilogy" that will document what happens to Spartan 117 after he is left adrift in space following the events of Halo 3. Below is a preview teaser released by 343 industries at E-3 2011 and a first look documentary focusing the development of the new game.
Halo four is slated for release in September, 2012.