http://www.cgtextures.com/
http://www.mayang.com/textures/index.htm
http://www.lemog.fr/lemog_textures/index.php
Those are the sites I use to find textures I use as a base in most of my work. So its a mix of hand made and stock image. I usually combine in layers several textures first to get the look I want, and then I take it further from there.