I hate the words “royalty free.” Most sites who advertise this way are not free at all. Despite this, droves of people flock to them to get clip art, photos, and music. The hard-to-discover ways these sites make money range from simply charging large up-front fees (not a royalty, after all) to much more devious things like restricting how you can use the content (such as not being able to use it in contests or not being able to use it online) to installing spyware on your computer as a part of their little gift to you (with your implicit permission, of course). Read the terms of use before you use these sites’ content, people!
Free does not mean open.
If you really want a free lunch of resources, look for content and software that is open licensed.