Muzei - Muzei is a live wallpaper that gently refreshes your home screen each day with famous works of art.
Magnus - Shazam for art
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
Artsy - A global platform for discovering and collecting art.
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
SINGULART - World's Leading Online Art Gallery