Now, this is good news! Caleb Kimbrough just launched Seamless Textures, dedicated to offer quality textures for free.
The site is divided into 9 sections : paper / concrete / fabric / grunge / clouds / rock / wood / grass / other.
When interviewed on colorburned.com, he simply explains:
High quality, high resolution textures are hard to find. If you wanted to, you could charge a lot of money for your images. Why do you choose to give these items away for free?
As Mr. Einstein once said: "It is every man's obligation to put back into the world at least the equivalent of what he takes out of it."