Also, my all time favourite book ever: Richard Matheson's 'I Am Legend'.
On top of that great choice, I'd recommend just about anything by Tom Clancy or Frank Herbert. Another of my favorite authors is R.A. Salvatore, for any who are into fantasy at all. And if you are... then of course you must read Tolkien.
But if I were to pick 4 of my all time favorite pieces of fiction, strangely they would be these...
The Walking Drum
Tarzan of the Apes
I've read better books, but these all had a significant impact on my early appreciation for fiction in general. Other honorable mentions, along the same line:
Conan the Barbarian (and the many additional books/short stories)
Fafhrd and the Gray Mouser (series)
The Sword of Shannara
Crikey... I could go on forever.
So many good books out there!