According to an article over on Yahoo (story), Steve Rogers' old sidekick Bucky Barnes took on the mantle (or bullet-proof shield in this case) of Captain America. While Bucky never swallowed the Super Soldier Serum back in 1940s (or at least he won't admit to the deed), he's donning a newly-designed suit, carrying firearms and bulked up while becoming a master of special operations (meaning he joined the Marines). Here's a bit more:
"We were toying with the idea of someone new taking over the mantle of Captain America," Quesada said by phone from his New York office. "But we kept coming back to Bucky. Not only because he seemed such an obvious choice but especially because of the fact that when we brought him back as the Winter Soldier he was so incredibly popular."
Actually Bucky has been a running character in the Cap comic for several years. When they relaunched Captain America a few years ago one of the first stories was the reveal that the Winter Soldier was Bucky.
Also the comic where Bucky was killed never actually existed in a first iteration. Bucky's death and involvement was retconned in later years.
It's even been hinted at that the Winter Soldier was involved in Wolverine's original escape from the Weapon X facility. Marvel just loves complicating their own continuity.