Here is a youtube video that demonstrates how to make a tileable texure in Photoshop.

http://www.youtube.com/watch?v=kjB7lYXqYFE

There is also this program called Genetica that generates tileable textures from scratch that you might find interesting.

http://www.spiralgraphics.biz/genetica.htm

Forum: Photoshop

Subject: How can I paint a seamless texture map for a 3D model with Photoshop?