Hello;
First post, glad to be here.
Some suggestions:
Free Flight by Douglas Terman (one of the best SHTF books I've ever read and nobody's heard of it).
Famine by Graham Masterton
No Blade of Grass by John Christopher
Vandenburg by Oliver Lange
Pulling Through by Dean Ing
The Camp of the Saints by Jean Raspail
The Last Canadian by William Heine
I, Martha Adams by Pauline Glen Winslow ( a little girl power in the resistance...)
Testament by David Morrell (early work by author of the First Blood series - Excellent)
The Rift by Walter J. Williams (fantastic)
The New Madrid Run by Michael Reisig
Damnation Alley by Roger Zelazny
The Postman by David Brin
Farnham's Freehold by Robert Heinlein
The Survivalist by Giles Tippette (Good stuff - the author was mostly known for Western themed novels)
Cold Creek Cash Store by Russell Hill
Wheels of Rage by Kurt Saxon (available free here -
http://www.kurtsaxon.com/wheels/chapter01.html )
I will post more when I come across them.