NASA Audio Collection   
Free to Use Sounds   
BBC Sound Effects Library   
Sound Bible   
NASA's Spooky Sounds of Space   
Dramatic Publishing   
Epic Sounds   
Free Sound.org   
Free to Use Sounds   
Pond5 SFX   
BBC Release   
Free Airborne Sound Effects   
Free Firearm Sound Effects Libary   
Echo Thief   
Free Sound Effects   
PacDV Sound Effects