Here are a couple of fun lampoons of classic monster posters. The first flips the situation in King Kong and presents the human as the monster, not really that far removed from the original in spirit if dramatically different in iconography. The second actually just shows the real world without the topsy-turvy threat posed by the awesome Tarantula in the movie of the same name. Now that was an awesome monster movie.
The organization responsible for these is UNEP (United Nations Environment Programme). Here's the website if you're interested.