http://everystockphoto.com is a wonderful search engine for finding free stock images! Search millions of images across a range of sites including Flickr.
http://www.openclipart.org is the perfect place to go if you are looking for illustrations rather than photos! choose from over 30,000 free images on this clean and easy to use site.
http://www.public-domain-photos.com This site has 5000 free photos and 8000 free cliparts for personal and commercial use.