DisplayFusion makes it easy to customize your desktop wallpaper with your own images. Select pictures from your own hard drive or pull them down from Flickr with this freebie. You can search for and preview shots from Flickr from within the program, and there are nice options for those with multiple monitors.
The straightforward progam window displays your monitor(s) in the top section, and you can click each one in turn to select an image for that monitor, or choose to have the background span both monitors. You can browse your own hard drive for pictures, but it's a good deal more fun to click the "Load from Flickr" button.
Doing so brings up another window where you can search for images based on keywords, particular Flickr Groups or a specific person. You can hunt for a person's shared images based on their name, or (a better bet) their e-mail address. Click any of the resulting thumbnail previews to select it as a background.
This fun utility is a free download, but a $20 Pro version gives you a nifty extra feature. The Pro version allows for randomly wallpaper changes using images selected either from your PC or from Flickr.
It's a cinch to use DisplayFusion, and the Flickr tie-in makes it much faster to pull down an online picture than going to the site and saving the image yourself. It used about 3mb of memory in my tests.