The File Open dialog has three very useful Media entries in the sidebar (Photos, Movies, Music). They are backed by the various iLife applications, so that you can select, for example, from your iPhoto albums.
The Finder windows have a "Search For" section in the sidebar, but the "All Images" entry there is just a smart folder that contains all image files from your whole hard disk with no further categorization.
Can I get the Media libraries to show up in the Finder as well?