I hope I'm not stealing Sgt. Art's thunder, but this is one of my favorites, too.
Amazon.com info here:
http://www.amazon.com/gp/product/04...002-2078968-7860021?n=507846&s=books&v=glance
In a nutshell, a comet collides with Earth and the novel follows a few groups of survivors in the aftermath. Unlike a lot of end-of-world novels, though, this one doesn't introduce the disaster (comet strike) until about 1/3 of the way in.
I hope this doesn't take the thread off-topic, but since I created it...
My favorite survival/end-of-world/apocalypse novels (in no particularly order):
A Canticle for Leibowitz
A Dusk of Demons
A Wrinkle in the Skin
Alas, Babylon
Day of the Triffids (MUCH better than the awful B-movie)
Dies the Fire (and sequels)
Earth Abides
Empty World
Hatchet (and sequels)
Lucifers Hammer
Malevil (rare European end-of-world novel)
My Side of the Mountain
On the Beach
Pendulum
Riddley Walker
Shiva Descending
Some Will Not Die (rare urban survival novel [as opposed to rural survival])
Swan Song
The Death of Grass
The Long Winter
The Odyssey Project
The Postman
The Prince in Waiting (and sequels)
The Rift
The Sixth Winter
The Stand
The White Mountains (and sequels)
The Wild Shore
Tunnel in the Sky
Warday
Wolf and Iron