We are discovering new types of planets constantly. Along with those mentioned, astronomers have discovered diamond planets (http://www.ibtimes.com/discovery-dia...y-world-847633
) and Hot Neptunes (http://www.centauri-dreams.org/?p=1263
Here is a real world list of planet types - http://en.wikipedia.org/wiki/List_of_planet_types
Like the situation with dinosaurs - where certain types of species will never be discovered because of where they lived, that there may be planet types that we might never discover.