There are small but useful compilation of websites with free HD textures and HDRI for CGI artists.

hdri

CG TEXTURES

textures.com (old wersion cgtextures.com)

allcgtextures.com

texturify.com

mayang.com/textures

opengameart.org/textures

texturelib.com

myfreetextures.com

openfootage.net

HDRI

hdrlabs.com/sibl/archive.html

hdri-skies.com/

hdrmaps.com/freebies