Very useful tutorial about creating tileable textures using Photoshop. When you have different shadow levels it seems a nightmare to fix it, but just a few of Photoshop steps to get it. Take a look to this (and others) tutorial by Neil Blevins
Probably you know textures.com (previously cgtextures) one of the most popular textures resources site. There you can find another tuts about textures and, of course, tons of texture for free or commercial. You only have to sign up.
