There are several ways to achieve a nice wood effect, but the one I am going to show you is pretty easy. The hardest thing is to get some good reference material, and to make you texture tile right. But if you have any suggestions for improvement, please tell me

In the zip file you will find a file called wood-texture with 3 layers. The first layer is the original reference picture, cropped to a interesting area. After cropping it you need to desaturate it (Shift + Alt + U). When this step is done, we need to make the wood tile-able. To do this go into Filter > Other > Offset – and offset the picture both on the x- and y-axis. Now you should clearly see the seam. The easiest way of  getting rid of the tiling, is to sample some pixels from the nearby areas with your stamp tool – until you have something like the last layer in the file. When you are done, simply select all, and go into Edit > Define Pattern, and type in the name of your pattern.

If you take a look at the file woodflat.psd – you can see the pattern applied, among other layer styles. 

And here’s another small example of what you can quickly put together using the same techniques.

If you have any questions, feel free to post them as a comment.