With the impending release of Cowboys and Aliens, which I understand is based on a comic book (?), I started to think of how many other movies or TV shows combined the Western format with Sci Fi. Of course I came up with the obvious - Joss Wheedon's Firefly. But it strikes me that some genres seem to meld together very well eg romantic comedy, historical romance, sci-fi thriller. And many genres don't meld often or well eg historical thriller (although I'm sure there are some good ones). Some genres seem to be diametrically opposed eg drama and comedy - although I'm sure the two have been cominbed to good effect occasionally. Another set of oppositional genres seems to be epics and thrillers because epic implies something that is long and drawn out and thriller implies something more fast paced. What are your favorite genre-bending movies? What are the most effective and least effective attempts at combining genres?