(I notice the < ul > tags are not supported here in this version either! Argh!
From the page: "...there are some clouds that are so rare that you will be very lucky to see them in your lifetime. This is a list of the top 10 most rarest cloud formations (in no particular order) that for those lucky enough to see them, were caught on camera."
Never thought of clouds as being quite this fascinating. These photos are definitely worth checking out.