Here are a few sites that offer free sound effects and music. But read the terms carefully. Most charge for use outside of home or classroom.
(For more, type “free sound effects” in Google or any search engine)
http://www.a1freesoundeffects.com/ A1 Free Sound effects.
http://www.freesound.org/ Free Sound Effects from Freesound.org.
http://www.stonewashed.net/sfx.html Sound Effects
http://www.partnersinrhyme.com/pir/PIRsfx.shtml Partners in Rhyme
http://www.videomaker.com/downloads/free-sound-effects/ Videomaker.com Free Sound FX