Freesound
freesound.org
A collaborative database of audio samples, recordings, and sound effects uploaded by contributors worldwide and licensed for free use.
Why it is useful
Provides a massive, searchable library of field recordings, instrument samples, and ambient sounds that would cost thousands to license commercially. For filmmakers, game developers, and musicians, it is an indispensable resource for production audio. The preview quality is high enough to audition sounds before downloading.