I stumbled upon the online gallery/"sketchbook" of Yoshihiro Moritake, and not only do I love the prints, but they are also available to download for free as desktop wallpaper! Just go to the "Gallery" section, click on the prints you like, and download the correct size.
Another great website is Pixelgirl Presents, featuring free wallpaper-sized versions of various artists' work. A couple of my favories are below. I especially love the ghostly watercolor cat.
And finally, Katogi Mari's gorgeous portfolio offers some free downloads, all in a brightly-colored, graphic representation of a fairy tale style. Check them out.