Poly Haven
This ‘Public 3D Asset Library’ provides great free Creative Commons textures in up to 4k resolution. Especially good medieval offerings with superb cobbles, bricks, tiles and stone. Funded by Epic and patreon to keep the content free.
GR Sites
Wide range of texture tiles perfect for retro and 8-bit style games and animations with a system to customise the colours to match your needs. Button maker and fonts too. The site hasn’t changed in 15 years.
Abaroth’s World
Clever random brick, stone and tile generator
Polligon
Includes some free textures and opinions on AI
Blender3D
blender.org/p/textures/ Texture Ninja
psdcovers.com/
Textures.com
lots of free content including photographs, textures and decals to add rust etc.