Spiral Graphics just started a new Blog on their site.   It has the intent of having more  How-to texture-creation tutorials.  They already have the following posts:

• What is a Seamless Texture (3D Texture, Tileable Texture)
• Create Custom Brick and Tile Patterns
• How to Import Models and Textures into Unity
• How to Make a Checkered Tile Floor Texture

Check it out!