My top sites and tips are:
- compfight.com Thanks go to Emma Coonan for pointing out this little gem. Set Creative Commons to 'only' at the top of the page to be sure of getting reusable content
- Images from Microsoft Office Clip Art is passé I know, but this site also has some great photos and backgrounds. It is easy to search by category, or refine your search using check boxes.
- Wikimedia Commons a huge database of freely useable media files which you can also add to yourself
- Imagecodr.org ImageCodr will generate ready-to-use HTML code for your web images. Takes the pain and hastle out of HTML code, licenses, attribution etc., etc,...
- Just search cleverly! Try a Google image search Then refine an advanced image search under 'usage rights' to pick up content that is labled for re-use. Same goes for Flickr Creative Commons where you can search under specific licenses