I use Flickr every day. It is one of those sites that has everything. I like to browser through the most interesting pictures, but find the 10-at-a-time interface too time consuming. FlickrLeech is a site that will show all 500 pictures on one page.
Retrievr lets you draw a picture in a “sketch” box and then do a search based on that shape. I can’t draw very well, but it is an interesting way to search.
http://labs.systemone.at/retrievr/
Slightlyblue’s site lets you pick a background color and then searches Flickr based on that color.
If you need some Create Common licensed photos and don’t like the 10-at-a-time interface, here are two sites that let you search only the CC licensed content and view all of them on one page.