Low Poly Rubble and the power of texture maps.
This isn't a tutorial so much as a 'learn by example' sort of deal. Here's two examples of rubble that I've created in the past.
Made Spring 2009
The example below is interesting in that this square patch of rubble actually TILES. You can take this geometry and snap it to it's side and all of the verts line up, and the texture lines up. This means that I can take this one square, tile it several times, weld the verts, and then go in with soft selection etc. and move and adjust it to create large patches of rubble that looks pretty realistic and diverse and all of this using only a SINGLE texture.
This smaller piece is created by taking a section of the above image, cutting out just the desired area, and moving it around to give it more mass.
To create this I actually made the texture map FIRST. I edited it in photoshop so that the texture tiled.
Then I took it into my 3d application (3dsmax in this case, but it really doesn't matter that much) and applied the texture onto a plane.
Then I went in and cut in the geometry detail to match up with the texture already placed on it.
I deformed the geometry up and down as needed.
That's basically it. Take it or leave it.