Attached Link: http://www.renderosity.com/viewed.ez?galleryid=170469&Start=1&Artist=Allen9&ByArtist=Yes

Look in the Bryce Free Stuff. Folks like Frank Allen are constantly posting great terrain materials. There's LOTS of them. One of the important things in getting mountains to look like real rock formations is using the Erosion button properly. First, when you create a terrain, or import a greyscale, leave it at the default 128x128 grid and hit the erosion button a couple of times. ALSO, hit the "slope noise" button a couple of times. Next, increase the grid size to 256 and repeat, then do it again with grid at 512, and then resize the grid one last time to the maximum of 1024 (Yeah it's big, but if you want good looking terrain details, you have to have enough points on the grid for it to work with) and hit the erosion button and the slope noise button once more. Note: the "size" of the erosion features change depending on the size of the grid you are using. Hitting 'erode' at 128 grid size puts in features that are much larger, in relation to the whole terrain, while doing it at 1024 puts in finer detail erosion. Experiment with this. Believe me, the combination of the erosion button and the slope noise, done at the different sizes, can really improve a mountain. I'm putting together a tutorial on this, with illustrations, and will be posting it sometime in the near future. Check the link to my latest pic. The mountains were created using this technique.