According to an announcement made by SEGA today, the game will come out next year. SEGA says the release date will be sometime in Spring, 2012 on the Xbox 360, PlayStation 3, and PC.
The game, being developed by Gearbox, aims to deliever some of the iconic elements of the Aliens franchise. Expect to fight against the relenteless Xenomorphs in claustrohpic environments that the films are known for.
Be on the lookout for more details on Aliens:Colonial Marines next week at E3.