If you can ignore the out-of-place religious references, this page has some awesome pictures and videos of Prandtl-Glauert Condensation Clouds (nice associated gallery here), wall-like clouds of condensation formed when aircraft are flying at transonic speeds. Jeff Wilkinson has assembled a good amount of information and links on the subject too, and there are other gallery sites as well. I think this example of the Space Shuttle Atlantis in the transonic regime is one of the coolest images, even if it isn't one of the more classic cloud shapes.