This free tool is handy for creating textures that tile without visible joins, both for 3D modelling work and as backgrounds for web pages etc'.
And don't think it can only do plain wood textures.
Here's one I made in a couple of minutes -
The tool itself is only a 4.5 MB download, if you would like a downloadable friendly tutorial video of it in use, this one is 130 MB -
This link shows a lower-resolution version of the tutorial, but also has links to hundreds of ready-made seamless textures -