Freesound - The Freesound Project is a collaborative database of Creative Commons licensed sounds.
Unity Asset Store - Unity's asset marketplace for game makers.
Mixkit Free Sound Effects - Mixkit Free Sound Effects is a website that is introduced for incredible free sound effects, making you use in your cinematic projects without any hurdle.
GameDev Market - GameDev Market is a marketplace for high quality, affordable 2D, 3D, GUI & Audio game assets, handcrafted by talented creators around the world.
Sample Focus - The easiest way to find the perfect audio sample
Kenney Assets - We've created over 40,000 images, audio files and 3D models for you to use in your projects. Thanks to our public domain license you're even allowed to use them in commercial projects!