According to the Rumor Mill section in the latest issue of EGM, Epic Games is currently working on Gears of War 3, which will feature a new "five player co-op experience." Based on the huge success of Gears of War 2 it's safe to say that this rumour is most likely true. And since Gears 2 already featured a five player cooperative mode (Horde), GamePro's best guess is that players will be taking control of Marcus, Dom, Baird, Cole, and Carmine in the single-player campaign.
EGM also claims that Epic is working on a multiplatform horror game, a rumour we've heard before but have no hard facts on. However, this wouldn't surprise us either.