"Unintended Consequences" by John Ross
Some read it for its historical aspects, as the first half of this classic novel by John Ross is a meticulously-researched compilation of how, over the past 90 years, the American gun culture has been transformed from the nation's mainstream to a "dangerous fringe group."
Others read it for the second half, which tells what happens when prototypical American Henry Bowman reaches his limit.
Once you read this book, you will not forget it.
UPDATE - 2/10/08: Download link removed as author Ross has indicated that all electronic copies of UC are unauthorized by him.