Well, my PC background changes like the tides, but at the moment it's based on the new 360 model. Mostly black but with shiny edges and the green lights.
On my laptop its stayed the same for about a year: A screenshot from the first Bad Company. It's one Abrams tank firing at another in the distance with an Apache shooting at the first tank. Everytime I see it I always think either two things: 1. That tank is going to die or 2. Always shoot the back of the tank.