Muzei - Muzei is a live wallpaper that gently refreshes your home screen each day with famous works of art.
New Tab by Flickr - Get a beautiful photo each time you open a new tab
Variety Wallpaper Changer - Variety is a wallpaper changer for Ubuntu which is featureful, yet slim and very easy to use.
Exposure New Tab - Get a beautiful photo from Exposure in every new tab
John's Background Switcher - Switch backgrounds to trending imgur, reddit, tumblr threads
Less Boring New Tab - Your browser deserves a better new tab page