Wood Tutorial for Photoshop
1.  Create a new file.
2.  Set Width to 256.
3.  Set Height to 1024.  (Note:  You can also use a different size here if you choose)
4.  Set the Foreground color to R228 G177 B123
5.  Set the Background color to R209 G161 B109
Note: You can also use my wood color swatches available in the 2d Freestuff area at 3d Commune or in the Photoshop Files section at tonylynchdesigns.com. The colors here are for Maple.
6.  Change the image size to width 2000% and height 50%
7.  Open the Image menu, select Canvas Size. Set the Height to 1/2 the Width (in this case 512). Click OK. Click Proceed.
8.  Change the image size to width 20% and height 800%
9.  Open the Image menu, select Adjustments>Brightness/Contrast. Set the Contrast to 5.
10.  Click OK
11.  Select Filter>Distort>Polar Coordinates
12.  Set it to Polar to Rectangular.
13.  Open the Filter menu, select Distort>Wave. Set the number of generators to 1. Set the wavelength to Min 10 Max 150. Set the Amplitude to Min 5 Max 15. Set the scale to 50% for both Horiz and Vert. Set the type to Sine. Set the Undefined areas to Wrap Around. Click on Randomize at least once, more if you want.