Wally is a cross-platform wallpaper changer which uses multiple sources for getting the images: local folders, Flickr, Google, Yahoo!, Panoramio, DeviantArt, Vladstudio, Photobucket, Buzznet, Picasa, and Smugmug images.
- change wallpaper manually / automatically (on a given interval)
- rotate images according to EXIF information
- set wallpaper position (centered, tiled, etc.)
- you can set downloaded photos to be at least 1/4, 3/4 or larger than the desktop size
- stores downloaded images on the disk so you can use them later on
Wally 2.4.2 was released a few days ago, finally getting GNOME3/GNOME Shell support. Also, the Bing module was removed because apparently Microsoft didn't accept Wally's way of using Bing.
To get Wally to work on Ubuntu, you need to whitelist its icon so it's displayed in the notification area - see THIS article for a complete how-to. But please note that in my test, Wally didn't work in Ubuntu 11.10 with Unity, even though it worked under the same Ubuntu version but using GNOME Shell (as well as Unity under Ubuntu 11.04).
Wally wallpaper changer works on Linux (KDE3, KDE4, Gnome, GnomeShell, XFCE4, Fluxbox and more), Windows and Mac OSX.
Download Wally (.deb, .dmg, .exe and source files; there are no .rpm files available for the latest Wally 2.4.2 yet)