Alright so I saw the movie adaptations for V for Vendetta and Sin City. I absolutely loved both movies, especially Sin City for it's cinematic comic book effects. I heard that Watchmen is soon going to be coming out on the big screen as well. Watchmen, along with the Dark Knight Returns, are supposed to be one of the best comic books written in comic book history, or at least it's reached a very high level of importance in the comic book world. So here's the situation, I saw the movies (plan on seeing Watchmen when it comes out), but never read the comics. Would it be worth reading V for Vendetta? Sin City? Watchmen? I was planning on going with the Absolute Edition for Watchmen. What exactly should I be looking for as far as the actual comics because I'm not sure that those movies were based on one specific book or on a range of books. In other words, I'm not sure if there's one book called Sin City which the movie is based off, or if it's an entire series called Sin City that the movie is based off (same goes for V for Vendetta). Either way any help is appreciated here.
Also are there any other comics out there like V for Vendetta (and Watchmen, even though I have yet to read it but I've heard only great things of it, plus its the same author)?