Guns and Legos are two of my favorite things in the world, so naturally, the coolest thing in the world are Lego guns (OK, not exactly a tour de force of logic, but humor me.) While the guns that Lego makes have gotten a ton better since I was a kid, they're still pretty lame.
Fortunately, BrickArms makes very sweet looking Lego guns, grenades, and knives (and a baseball bat!) as well as some custom mini-figures for your Lego combat action. I especially love the Halo themed weapons. Anyway, check it out.