I'm willing to have anything as my wallpaper, so long as it's not pornographic or related to anime (am mostly afraid of being judged by others if I have anything set from these kind of categories, in a way).
Right now, what I have on my laptop is a cat artwork, with dark-purple texturized background. This came pre-downloaded with my Ubuntu installation, and it's simply adorable, at least in my eyes! I've had it for about six to eight months in total now; long time. Thankfully, the wallpaper doesn't seem to grow tiring at all.
Prior to above, I've had something displaying fireworks, with shades of yellow, orange, red, and pink. It was beautiful. As for which website I use to grab wallpaper, most of the time, it's deviantART.