Top Dog http://www.topdogwebs.com/audio_effects.html
School Site http://www.schoolsite.edex.net.uk/500/waves.htm
Koumis http://www.koumis.com/soundfx.htm
Partners in Rhyme http://www.partnersinrhyme.com/pir/PIRsfx.html
The Wav Place http://www.thewavplace.com/
Media Tracs http://www.media-tracks.com/soundeffects.asp
Sound America (Teachers only should use this one. Needs to be previewed) http://www.soundamerica.com/