Retaining walls can be made from all kinds of stone and still get the job done, but if you are trying to make a statement think about using reclaimed granite. The material comes in many shapes, sizes and colors. The previous uses of the material ranges from cobblestones up to old bridge abutment blocks that were used before reinforced concrete became more cost effective.
I drove past this wall today and just had to stop and take a picture. Look at the range of size, colors and shapes. This is a very handsome and completely function wall. Give me a call if you'd like to incorporate something like this into your project. Gavin