Extra credit
How about books or movies that have actually addressed this issue, (without zombies)?
"Lucifer's Hammer" comes to mind in books, as does "The Postman," which was reviewed on the same site as ER's link. "Alas, Babylon," treats post-nuclear-war civilization a lot differently than "On the Beach," and in fact, I've found a lot more optimists in SF than pessemists.
In movies, oddly enough, I think "Road Warrior" touched on this concept fairly well, although we see mostly the predators (more exciting) and not enough of those trying to rebuild things.