Music and Sounds

A1 Free Sound Effects

Absolute Sound Effects Archive
CC Mixer (download and share hundreds of sounds)

ClipArt.com (free, but register)

FindSounds
Free Audio Clips (select from many categories) 
Free Kids Music (complete songs; quality kids music; free downloads)
Free-Loops.com

Free Sound Effects

Free Sound Effects

Free Sound File Archive from TNS

FreePlayMusic (great for background music and sound tracks)

I Love Computer

JungleWalk

Listen to Nature
Mixture of Sounds (dozens of sounds perfect for interactive whiteboard activities, PowerPoints, movies, etc.)
Music Directory (good collection of sound clips)
Nature Songs (wonderful collection of birds, nature, and animals)
Section Z (great place to find sounds)

Simply the Best Sounds

Sound America (songs, quirky things, and sound effects)

SoundDogs
Sound Effects Library (scroll down for free sound effects)

Sound Jay
Soungle - FREE audio of all kinds

WavCentral.com