For the past few years Nintendo has been offering desktop wallpapers for their more "important" games as part of various marketing campaigns.  Typically these images were offered up for free downloads on a game's promotional website or were offered as small prizes for completing a simple online challenge.  A few were even kept locked away with the key to access being a purchase of the respective game that was the source of the artwork.  The problem is that once these games have done their job in the marketplace, the promotional material just sort of fades away.  Do you honestly expect to easily find wallpapers from, say, Luigi's Mansion or Mario Party 4 after all this time?  Thankfully there's The Mushroom Kingdom and its relatively new archive of promotional wallpaper.  Most of your favorite Super Mario-related wallpapers are there in a variety of sizes to fit your monitor.  I'm partial to the Mario Kart DS images, but I'm sure you'll find something you like.