Check out this great Wallpaper Manager for Windows 7 from MSN. Its a 13MB download, which includes some great walls too.
MSN Wallpaper Manager
The installer will ask you if you want to make Bing search as default, make MSN your homepage. Take your decision and un-check/check options if you have to.
You can crop, rotate, resize,edit, flip, add graphic elements or text, change settings, insert foreground images, create a slideshow of images and do a lot of things with it. Once you have created your wallpaper, set it as your desktop wallpaper. Now navigate to hidden folder C:\Users\username\AppData\Roaming\wallpapers\user\complete. You will be able to export the saved walls from this folder.
Quite a nice app, actually ! Using it I made a Wallpaper for The Windows Club. Want to download it and check it out? Do note that the background wall is not my creation. I just put A & B together to create it, to show how simple it is to use.
Visit MSN to download it for FREE! (UPDATE: It appears to have been taken offline).
You may want to have a look at WallSlideShow, a free Wallpaper Manager to manage vast collection of Wallpapers.