You can go the route of modesty with a gaming rig—sure, but there's something to be said for the glowing, flowing, completely outrageous rig of conspicuous PC carnage. How about a motherboard that looks like a disassembled gun?
The Gigabyte G1.Assassin straps enormo-heatsinks in the shape of barrels and a full magazine. And it looks surprisingly cool, and surprisingly not-tacky! The gunmetal heatsinks will look great if you've got a window on your case—otherwise, there's not really much point to the commando adornment. On the other hand, it's still a solid (albeit massive—XL-ATX) Gigabyte motherboard, providing eight USB 3.0 ports, room for an i7 CPU, support for 4x CrossFire or 3x SLI graphics, onboard Creative X-Fi, and built-in Killer NIC E2100 ethernet. Although the latter is of highly dubious value. All this doesn't come cheap—$530 is a shit-ton for a motherboard.
But how many motherboard can you take apart and build into a machine gun? Not this one: "Heatsink: Not a weapon. Cannot be assembled as a weapon." Ugh. [Gigabyte via MaxPC]