If you ever needed a good texture for a scene, you probably know that good texture library is very important for any 3d artist. Even if most professionals recommend not using pre-made textures, we need something to get started. A good place to get started with textures is a website called Texture Archive, which offers a lot of free textures.
All textures there are organized into categories like:
This is just some of their categories. They even have UV Grid Maps available to download! And the textures available have a good resolution. They say that small textures are 2592 pixels wide or less.
Even been free to download, they kind of control their bandwidth by giving each user some kind of credits, called tokens. When your first sign up, you receive 1000 tokens and when a texture is downloaded, some tokens will be subtracted from your account. If you get yourself without any tokens, then you will have to wait until the next month to receive more.
If you want to check their collection, visit Texture Archive. Remember, even been free you must register to download any file. But, it`s a nice resource anyway.