It's probably been mentioned, but ONE SECOND AFTER by William R. Forstchen is outstanding.
Basic premise: Unknown 3rd party biffs several nukes above the Ionosphere, setting up a massive EMP that blows North America back to the high middle ages, technologically speaking. If it had anything to do with electricity, forget about it. The bits about die-offs coming in waves I found to be especially interesting... the "why" behind them and then how to possibly prevent them... or mitigate them.
Best case survival percentage one year after an EMP blows out the grid? 18%.
It's a good read.