Ah, where to begin...
1) The Moon is a Harsh Mistress - Robert A. Heinlein
2) The Idle Warriors, by Kerry Thornley
This is a really rare one, but it's interesting from a historical perspective. You see, the author was friends with Lee Harvey Oswald, and the book was written about him. In 1962. It was published six years before Kennedy was shot.
3) The Heart is a Lonely Hunter - Carson McCullers
4) Flowers for Algernon - Daniel Keyes
5) In Our Time - Hemingway
6) The Way Things Work - David Macaulay
This is a huge, illustrated guide to just about every machine you can think of. I'll never again have to wonder about how a pocket watch works, because it's been explained to me in detail by cartoon mammoths.
7) Abel's Island - William Stieg
My first favorite book
It's one of those books that's "meant" for kids, but the older you get the deeper you realize the book is. It's by the same guy that wrote Shreck.
8) Saint Jack - Paul Theroux
I just really identified with the main character... dunno if anyone else would like this one
9) DK Pocket World Atlas
A few years ago, I just carried this thing around with me for a week or so, and I'd just whip it out whenever I had a few minutes, waiting in line, waiting for the bus, etc. After just a few days I was able to bring up a world map in my mind, just from memory. To this day, when I read the news I never have to stop and wonder "Hey, I wonder where Liberia is, exactly?"
10) English as she is Spoke, by José Fonseca and Pedro Carolino
Once upon a time, these two publishers in Portugal set out to make an English-Portugese phrasebook. All they had was a Portugese-French dictionary and a French-English dictionary. The result is "English as she is Spoke". It reads like an experiment in surrealist free-writing; "The noise run that is to him not the a thing by man"...
Now, I'd never make fun of someone for not speaking English (their English is still waaaay better than my Portugese) but I like to keep the book on my shelf to remind me of things like cultural relativity and the danger of direct translation... so it's a book with an unintentional moral