It seems one can track the socio-economic trends in popular culture by the appearance of either Zombies or Vampires showing up in our consciousness.
Right now we seem to be in Vampire overdrive with the Twilight series and HBO's True Blood though Zombies have been making a steady showing in films such as Zombieland and in remixed versions of classic literature with Pride and Prejudice and Zombies. Either way, the monsters are among us, either sucking us dry or eating us alive.
Vampires are the monsters of our intellect. They suffer our existential dilemmas, some even our guilt and shame. They are the ultimate prisoners of body consciousness. Trapped in an eternity that mortals always tend to romanticize because we are (as yet) incapable of living for centuries. In Freudian terms, vampires are the super ego made manifest. These graceful dandies drive fast cars as they struggle to control their carnal desire for human blood. You can find a comprehensive history of vampires here.
Zombies on the other hand can be seen as manifestations of the id. Zombies are dim-witted, staggering louts, poor conversationalists. They are anonymous, remorseless, endless in number, viral. They are all about self-gratification, excess, engorgement, acquisition of more. And oddly, any organized authority is unable to stop them. Zombies are only defeated by a rag tag band of individuals teaming up together to wipe our their scourge - one gore-spattered shotgun blast at a time. What better Zombie movie has there ever been than George Romero's Dawn of the Dead where a shopping mall is the common ground. Zombies frantically search for food in a lusty frenzy while the living are holed up, determined to cling to their last outpost of humanity? A cinematic Zombie timeline is here.
Zombies and Vampires are us, transformed version of humans, our monstrous selves. Writers and artists have used them as metaphors for our political, social and economic fears. They stand in for despotic regimes, our psychological terrors, fears of the other and fear of intimacy, for miscegenation, sexism, xenophobia, communists, homosexuals, consumers. Our fears concerning sexually transmitted disease, mental illness, technology and class division have all been addressed by these fantastic creatures of our mind who define and create by destroying others. If one looks back over the 20th century, it's possible to view the boom times through a filter of Zombies (1950's, 1980's) and the bust with Vampires (1970's, 1990's) so the trend would appear cyclical and somewhat predictable. Which ever genre has the upper hand, there appears to be no end to our monster mania as long as we remain human.