Sound Effect Downloads
Freesound.org - download a variety of sounds for use in videos. Need to create an account to download sounds.
Sound Bible - I've heard good things and it's Creative Commons licensed
ZapSplat - Free Sounds. Can use this account.....Login: gmscomputers password: rocket
FreeSoundEffects.com - Scroll down and look in the left column for the free ones.
AudioMicro - More free sound effects. Need an account to download sounds.
More possible sound sites - A blog about sound effect sites