I have always wanted to keep a themed sketchbook, but never was sure what the theme could be. Recently I came across something in one of the blogs I follow, and decided to jump in... WATERCOLOR SPLASH MONSTERS YAY. So fun. The best thing about drawing these is that you don't have to plan on anything, The Monster appears on its own!
(Now that I think about it I have already started a themed sketchbook. Remember the Mayan Glyphs?)