I will add more as I find them. Feel free to also post replies with more resources, but if they are not public domain, please mention what license they use.
https://freesound.org/ = Freesound is a collaborative database of Creative Commons Licensed sounds.
http://soundimage.org/ = This site contains original music, sound effects and images created by Eric Matyas , which you are welcome to use in your projects (commercial and non-commercial) with proper attribution to the creator.
