One of my favourite blogs is Bobby Solomon's Kitsune Noir. Once a week, Bobby posts a new desktop wallpaper that has been sent in by an independent designer, illustrator, or artist. This Desktop Wallpaper Project has kept my desktop looking ace for like the past 6-8 months.
There are different resolutions for different desktop sizes, and the style of the design changes dramatically each week, and with work from guys like Tavis Coburn, Josh Cochran, and Rey Ortega, the work is top-notch. Check out a few examples below, and definitely have a look at the site for the full range of wallpapers: