I'm fine with the occasional "I'm one of the sole human survivors in a world full of freaks trying to kill me" movie, but with 28 Weeks Later just out and I Am Legend and 30 Days of Night on the horizon, this is getting to be too much. You can now add The Invasion to the list, as Nicole Kidman runs panicked from the masses of invaders trying to recruit her into their invading army.
If nothing else, though similar in theme, these films should provide good support for parents trying to teach their kids about the dangers of peer pressure. First, talk to your kid about not using drugs "just because everyone else is," but make sure you sneak something in at the end about how drugs "suck the life from you like a vampire," or "are an alien force that takes over your body." Then take them to see the corresponding movie for your simile.
Another option is to take them to Shrek 3 with the message, "See? If you were screwed up on enough drugs you'd probably be enjoying this, at least marginally, and wouldn't that be embarrassing?"