CC0Textures.com offers a library containing hundreds of detailed PBR materials with displacement-, normal- and roughness maps in resolutions of up to 8192px for photorealistic rendering. The assets are available under the Creative Commons CC0 License. This means that you can use them for free for any purpose (even commercially!).
Check out the latest releases!
The library is growing constantly. New textures are added all the time, here are the latest creations: