Lots of people seem to be posting texture tutorials, so I thought I'd do a quick one (designed for PS):
1)Start with a blank canvas (512x512)
2)Choose a background and foreground color for the two shades of your stone/cave wall. Greys and Grey-browns work well.
3)goto filter>render>clouds
4)Now add a little monochromatic noise for variation (not much).
filter>noise>add noise
Now your texture should now look like this:
5)Goto window>show channels. Click on the 'Blue' channel, and drag it to the copy icon (the little page at the bottom right of the floating window)
6)press control-a and delete to clear this new channel. Double click the new channel and rename it to "Stone Bump" (or something similar)
7)Make sure black and white are selected as foreground and backgroud (press 'D' if they aren't), and goto filter>render>clouds.
8)Now go to window>show layers, and click on the main layer
9)goto filter>render>lighting effects.
Use settings similar to these:
10)click ok, and now the texture is basicly done. Adjust the contrast and brightness (in the image>adjust menu) until it looks just right. Also experiment with different lighting angles. So long as you use a directional light, the texture should automaticly be seamless. Also, you may want to adjust the height and intensity for ingame use, becuase too dramatic lighting can conflict with scene lighting and look funny. Enjoy!
edit:
Taadaa!
Also, some of the best texture tutorials sites I've found:
http://www.lakesdigitalarts.com/content.php?id=p4
http://div.dyndns.org/EK/tutorial/
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