http://www.manucornet.net/Informatique/Texturize.php
The new 2.0 version finally creates tileable textures out of any given image. And it looks pretty much perfect if the brightness is uniform. Its really impressive… check the screenshots for yourself! 
Ohhh, genius! That’s excellent.
Cas 
Excellent! I was looking for one of those. Thanks for the heads up!
The windows build:
http://www.manucornet.net/Informatique/Progs/texturize-2.0.zip
[i]After downloading the Windows version of the plugin, just unzip the file and put it into your GIMP plugins directory. The plugins directory should be located at C:\Program Files\GIMP-2.2\lib\gimp\2.0\plugins (replace the beginning of this path by wherever you installed the GIMP program).
Then quit The GIMP if it was open, and launch it again to let it load the new plugin.[/i]
All I had to do was molesting the guy who made the previous build