This list is focused on VR development.
This post could be updated in the future.
Assets
Building assets from scratch is one of the most troublesome work we could avoid as a developer. Unity asset store shares lots of libraries for us, but there are other supportive platforms as well. Keep in mind that some are not free and shall be credited. I have learned about them through Justin P Barnett’s VR Academy.
3D Arts
turbosquid.com
free3d.com
cgtrader.com
sketchfab.com
unity.com/features/probuilder
Textures
sharetextures.com
ambientcg.com
sketchuptextureclub.com
polyhaven.com
Audio
freesound.org
epidemicsound.com
pixabay.com
soundbible.com