Muzei Live Wallpaper is a free app from developer Roman Nurik. His name may sound familiar, as he is also the developer of the popular DashClock widget.
Taking the same approach that he took with DashClock, Nurik has made Muzei Live Wallpaper free and open to developers to integrate with various services.
After installing Muzei, you'll have the option to select a service from which the app will pull random images. The default option is featured art, updated once a day. You can also select a photo album on your device, and increase the frequency of your wallpaper changing, if you so desire.
Perhaps the best part about the app, beyond its price tag, is the fact that it's API for third-party developers. Meaning, if someone wanted to create a Muzei plug-in to bring Instagram photos into the service, it's possible. In fact, it's already been done.
Searching the Play Store for "Muzei" will reveal a lengthy list of plug-ins. A sample list of the more notable services includes Dropbox, Reddit, Flickr, 500px,and Tumblr.