This Ultramarines Bolt Pistol is a replica of a gun from Ultramarines Warhammer 40k, an upcoming movie based on popular video game series Warhammer 40k. It is really well done and truly impressive, even more given the fact its creator made it in 9 days.
Other weapon replicas inspired from video games:
Fallout 3 Plasma Rifle (36 pics)
Team Fortress 2 Shotgun (31 pics)
Mass Effect Rifle (61 pics)