All pictures, sounds, videos words on the internet are copyright, which means they shouldn't be copied without asking permission and possibly paying for it.
All the resources below are royalty free (ie, the copyright has been given up) and are also free to use.
Look also for creative commons resources.
Sound effects and sound loops - copyright free
Flashkit loops http://www.flashkit.com/loops/
Flashkit sound fx http://www.flashkit.com/soundfx/
Partners in Rhyme. http://www.partnersinrhyme.com/pir/PIRsfx.shtml
PIR sell copyright free music, but this page has samples of their FREE sounds.
http://www.findsounds.com/ (this is a cheat - these are not copyright free necessarily, but a very good search tool for sounds.)