According to Wikipedia, “Royalty-free, or RF, refers to the right to use copyrighted material or intellectual property without the need to pay royalties for each use or per volume sold, or some time period of use or sales.” Below are some sites to use to gather royalty-free pictures and media:

Images:

• Google Advanced Search (scroll down to “usage rights” and adjust your search criteria appropriately)
• Getty Images (Here’s an article about this feature)
• Wikimedia Commons
• Creative Commons
• Flickr: Creative Commons
• Open Clip Art

Music:

• Incompetech (AMAZING site – much of the music on this site would not sound out of place in a Hollywood film.)
• mobygratis – Apply to use Moby-created music in your non-profit project