of the top of my head, here's my ten best:

The Decline and Fall of Practically Everybody - Will Cuppy
Cat's Cradle -Kurt Vonnegut
The Red Queen/Sex and the Evolution of Human Nature - Matt Ridley
Stranger in a Strange Land - Robert A. Heinlein
The World According to Garp - John Irving
Sex in History - Reay Tannahill
Backlash - Susan Faludi
Hitchhiker's Guide to the Galaxy - Douglas Adams
Skinny Legs and All - Tom Robbins
The White Hotel - D. M. Thomas

oh yeah...FIDDY

a few more:

Crime And Punishment - Fyodor Dostoyevsky
The Manitous - Basil Johnston
The Sex Life Of Plants - Alec Bristow
Fugitive Pieces - Anne Michaels

an awesome talent, dead at 39. Why couldn't it have been Dean Koontz instead? Hacks live forever, the great ones die young..

as long as I'm posting in this thread again:

Fahrenheit 451 - Ray Bradbury
The Jungle - Upton Sinclair (this book is one of the few that changed my entire world view)

Neil Gaiman is a good new writer, I was very surprised to find out I liked westerns when I read Lonesome Dove by Larry McMurtry, I immediately went out and bought everything else I could find by the same author. Soul on Ice by Eldridge Cleaver had an impression on a young dig420, and The Archipeligo by Alexandr Solzienitzyn (sic) was pretty moving too.

Summer of 42 by Herman Raucher is the best 'coming of age' novel I've ever read, Piers Anthony and the Xanth Chronicles are great for young readers. Older SF fans HAVE to read The Chronicles of Thomas Covenant, Unbeliever and also Roger Zelazny's Amber series.

The problem with great books is that it's hard to stop, I always think of one after I post that it's just damned disrespectful to leave out of the list :1orglaugh

One Day in the Life of Ivan Denisovitch - Alexander Solzhenitsyn
Diary of Anne Frank

Grisham and some other 'thriller' type authors actually have teams that write their books for them, they just edit it and sign their name to the manuscript. I can't get into him for that reason. You don't actually know whose work you're reading.

howard stern's miss america
red mafiya
the hot house:life inside levenworth prison
99 crucial shots of pool
wiseguy

all of stephen king
good portion of john saul
gotti (and a few related to this area)
to kill a mockingbird
barbarians at the gate

Sorry, but those don't qualify as Dune books.

My top 5 favorite books:

Dune
Children of Dune
Heretics of Dune
God Emporor of Dune
Chapterhouse Dune

What I mean, by the way, is just that Brian Herbert isn't half the writer his father was. The original Dune books changed the way I look at the world... powerful books. The prequels just feel way too simplistic to me.

This is difficult because a book that might have been very influential in my life a decade ago may seem not worthy now on the face of it. I'll just go with these.

Influence (Cialdini)
Asimov's Guide to the Bible (Asimov)
Fear and Loathing in Las Vegas (Thompson)
Lolita (Nabokov)
The Republic (Plato)

Google Hacks
The Answer Is Always Yes
Ishmael
Do Androids Dream Of Electric Sheep?
One Fish Two Fish Red Fish Blue Fish

FierFly - Piers Anthony

Som Of All Fears - Tom Clancy

It's hard to list all my favorites.
Swan Song
Deep Lie
Carrion Comfort