Read the Dream Quest of Unknown Kadath, courtesy of the Dagon Bytes website.
I found this picture of Moonbeasts at 3x6.net. I can't read the text because it is in French, and I am tres illiterate in French. There are a lot of great pictures on the site, and if you can read French, you will be so much the happier to visit.
The moonbeasts dwell on the dark side of the moon. They travel both on water and through space in great black galleys and enslave, consume, and experiment on beings of other races. They serve Nyarlathotep.
Moonbeasts are generally thought of as being utterly hideous in appearance. However, at least one writer postulates that they are adorable but nonetheless sadistic and bloodthirsty, such as this one seen in the picture below (available from Pen and Paper RPG Shop)
Read Ian Klych's account of the wicked and horrific exploits of the bloodthirsty and sadistic yet disturbingly cuddly Moonbeast.