During the production of a game, a lot of concept art gets drawn up, redrawn, thrown away, cursed at, and, occasionally, even used. There's a mountain of this stuff fluttering around the Valve offices, and while the non-artists among us might not know much (anything) about art, we hope we're not embarrassing our artists by saying it looks pretty kickass. So we grabbed some of it off the nearest pile and made it into desktop wallpaper: