Texture library THE reference: textures.com The biggest texture database for 3D.
Sketchup Texture, quality textures.
HDRI Haven, the site that offers high quality environmental images at affordable prices!
Free high quality images and photos: Pixabay.
Tollens color chart for SketchUp: totem, totem facade and urban color and mood.
Spherical HDRI images to enhance the realism of your renderings.
Texturer : textures site, similar to CGtextures.
Plaintextures : a free high resolution textures site.
sIBL Archive: HDRI images for the environment.
openfootage : big pack of materials.
Polantis for textures from pro catalogs.
CGSkies for panoramic sky textures.
https://www.designersguild.com to find wallpapers and fabrics.