As I have no doubt that you've already hurried out to see the Watchmen, I respectfully submit some reading suggestions to follow up the experience.
First, cleanse your palate with Superman: Brainiac (by Johns and Frank). This is a straight up, mainstream, super-hero adventure. But . . . Johns captures a sense of grandeur and a depth of emotion that will catch you by surprise. He manages to capture the best of Superman, making the book feel both classic (recalling the feeling of Superman: the Movie, in particular) and completely fresh at the same time. This has got Superman and his cousin Supergirl facing a terrifying threat from long-dead Krypton in a battle which has unexpected, and tragic, repercussions. It doesn't hurt that Frank's figural work and action are about the best in modern mainstream comics. I swear, you will be able to hear Christopher Reeve speaking when you see his Superman.
Then, dip into something decidedly darker and stranger with Omega the Unknown (by Lethem and Dalrymple). Novelist Lethem updates the obscures 1970's hero with the story of an alienated teen who starts off by learning that his recently deceased parents were actually robots and ends up with a connection to one very, very unusual super-hero. Intelligent, disturbing and filled with characters that are complex in both motive and morality, Omega is one of Watchmen's worthy successors.
Finally, if the movie has prompted you to take a look back at your much-thumbed or brand new copy of Watchmen, here's something you might not have noticed. Chapter 5 ("Fearful Symmetry") is perfectly visually symmetrical. The first page composition and color scheme matches that of the last page exactly. The second page matches the second to last, and so on, right to a dramatic meeting right in the middle. Just one more way that Watchmen used the sequential art form like nothing before it ever had.
Hopefully, this will keep you until you head back to the theater for a second viewing.