My gun is kind of a sword. It's more for cool factor than practicality, honestly. It's like the Lancer from from Gears of War, but instead of a chainsaw it's a static blade running pretty much the entire length except for one small par to put your hand on to aim and instead of an assault rifle it's a low-powered bolt-action rifle, built to be as light as possible. The magazine is on top, too. It's primarily meant to be held and used like a sword. It doesn't work very well, but it looks pretty cool. Also, it's only a drawing.
For awesomeness, I'd choose a handgun that tears holes in reality, like a Portal Gun. Unlike the Portal Gun, it can create these holes in air, instead of just on surfaces and I can use it to send bullets and other miscellaneous objects flying at my adversary with the portals.