Zen Textures and Lost & Taken are two places that I've found some nice backgrounds at. The images, I think, are high-res enough for a 1440x900+ screen res to comfortably fit these images. I'm fairly certain that I snagged a wooden background for my character, Johnathan, from Zen Textures and it looks rather nice for a centered table-like layout (which the Generator layout looks like/is similar to).