Pete Corp has built a very cool sniper rifle that, though it's not quite minifig-scale, is surprisingly compact considering the amount of detail that has managed to pack into it. He didn't specify what type it's supposed to be, but it looks like an Accuracy International Artic Warfare to me. The photography is also excellent, though according to the photo's description on flickr, it's due to the fact that the builder was lacking some parts in black. My only gripe is that the scope is a tad tad too short, but building realistic weapons at this scale is no easy feat, so my hat is off to Pete.
Meanwhile, an obviously very talented builder by the name of Giovanni Tuzzi (apparently relatively new to the flickr scene) has been working on a life-size Dragunov sniper rifle. Life-size weapons built out of LEGO bricks seem to be one of the more popular things that people choose to build when it comes to military-themed creations, but this one really stands out to me. It's hard to tell that it's not real at first glance, and upon close inspection it's accurate down to just about every last detail.