Variety is a wallpaper changer application that works with most desktop environments (KDE, LXDE, Xfce and Unity / GNOME Shell) and, besides being able to change your wallpaper automatically on an interval you set or on demand, the application can automatically download wallpapers from Flickr, Wallbase.cc, Wallpapers.net as well as NASA Astronomy Picture of the Day.
Other Variety features:
Ubuntu appindicator support; you can scroll over the indicator icon to change the wallpapercan apply fancy filters to the images: grayscale, heavy blur, oil painting, charcoal painting, pointilism, pixellateoption to display the time on the desktop, using a nice digital clockclipboard support: can monitor the clipboard for image URLs and fetch themmore
There’s also a cool preview feature in the style of Google Plus – when clicking on a wallpaper source, you get to see a preview of all the available wallpapers on the bottom of the desktop (see screenshot from the beginning of the post).
Variety 0.4.10 has been released recently, with new features, like support for RSS Feeds which means the application can now automatically download wallpapers from a lot more websites, including Picasa, deviantART and so on.