Check out this great Google Cheat Sheet. You will probably find some really useful tips to help you find exactly what you are searching for. Enjoy!
Creative Commons is a non-profit organisation founded on the notion that some authors may not want to exercise all of the intellectual property rights the law affords them. Creative Commons has developed a set of free public licences to enable authors to share their work with others. http://creativecommons.org/
Search page for creative commons images: http://creativecommons.org/image/
Here is a list of other websites where you can find photos and images: http://www.masternewmedia.org/news/2005/04/01/where_to_find_free_images.htm