I couldn't pass the opportunity to mention our rifle the XCR. The whole SCAR program came out of work Robinson Armament Co. did for USSOCOM. The XCR, though not as well know, is worth a try if you want a really innovative next generation battle rifle.
While the SCAR and ACR work off a Stoner type bolt system, the XCR uses more of a Kalashnikov type system. The XCR works flawlessly in several calibers such as 5.56, 6.8, 7.62x39mm, and 5.45x39mm. Recently, we began shipping the XCR-M in .308.
You can check these rifles out at Robinson Armament Company - Official Homepage