Iain Andrews' site Steam Postcards has long been my wallpaper supplier of choice. Why? Because he plays games and takes screenshots that aren't the kind of thing you'd find in a magazine or popular internet video game website.
He instead takes, well, postcards. Scenic shots of the background, or the walls, or the sky, or whatever, finding stuff that just looks good, instead of stuff that makes the game look good.
His current subject of choice is id's RAGE, but scroll down the Tumblr page and you'll see games like Deus Ex: Human Revolution, Mirror's Edge, Mafia II, Team Fortress 2, Red Orchestra and even Kane & Lynch.
The images maybe aren't nice enough to print out and frame, but like I said, they're perfect for wallpapers!
Steam Postcards [enwandrews]