CG-Source.com is a site dedicated to deliver the highest quality textures possible. The quality and resolution is unmatched by any other site. The current average resolution is 101 megapixels per texture.
Furthermore, free tools like the FloorGenerator and MultiTexture Map is given away for free to help improve your renderings.
Feel free to browse the site, if you want to sign up to the mailinglist then just register on the site. When you are registered it is also possible to download tools and buy credits so you can start downloading textures.