Viewfinder brings powerful Flickr search to your Mac
A native Mac OS X application (requiring Mac OS X Snow Leopard), Viewfinder allows you to search Flickr from the desktop apply filters to show only Creative Commons images, and specify a particular image size. Then, once you select an image you can download the image, set it as your desktop background - and most importantly - send images straight to Keynote for your slides.
If you're a heavy keynote user (or blogger) who frequently needs to find Flickr images for your work Viewfinder is indispensible. I've been testing it since early September and found it an incredibly convenient tool to have at hand. A licence costs £15 (roughly $25) and a free demo is available for you try from the Viewfinder webpage.