Wallch: Wallpaper Changer For GNOME 3 / Unity

Wallch is an automatic wallpaper changer that works with GNOME 3 (and Unity). It features desktop/sound notifications, random image and time changing, live earth wallpaper (a 'live' picture of the earth updated every half hour), taking screenshots or webcam image.

The application also comes with Unity launcher support, so you can start or stop Wallch, select the next or previous wallpaper or start the live earth wallpaper from the Unity launcher: