To help break up the monotony of the current mesh set, I have made a full set of additional wall meshes, here:
http://opengameart.org/content/3d-rock-tileset
It is based off layout.blend, I did not have the licence information so was unable to credit the author immediately on OGA, if someone could provide the original author i will gladly credit them on OGA.
I understand you may eventually implement a randomised wall system, however this is to help tide you over until then. It may also help with the other room tilesets which still remain to be done.