1. Angels and Demons, by Dan Brown

Read that text.  If you have the software, download the image and rotate it 180 degrees. If you don't have the software, stand on your head and look again at the image. Notice that you can read "Angels and Demons" both ways. Come on, that's just cool.
 

This book recently replaced "Ender's Game" as my favorite book of all time. It is a conspiracy/terrorism thriller/mystery/historical fiction/science fiction, and if you enjoy any of those genres, or just a good story, you'll like Angels and Demons.Terrorists in the near future threaten to destroy the Vatican with a high tech weapon. The terrorists are members of an old secret society, the Illuminati, which has long been against the Catholic church. To stop them, a Harvard professor must search through the paintings and statues of Rome and the Vatican for clues to where the Illuminati stronghold is. All sorts of cool technology is thrown into the mix, just to make Angels and Demons even more awesome.
 

Also recommended by Dan Brown: The Da Vinci Code (sequel to Angels and Demons) , Deception Point,  Digital Fortess.
 
 
 
 
 

2.  In a Sunburned Country, by Bill Bryson

Bill Bryson's delightful travelogue of Australia is a must for anyone going down under, or just for anyone who wants an amusing read. His descriptions of the history, culture, and animal life of Australia are insightful, interesting, and usually downright funny. Few people know as much as we should about the only country that's also a continent, and this book is a fun way to change that.
 
 

Also recommended by Bill Bryson: A Brief  History of Nearly Everything (a description of the formation of the universe, earth, life on earth, and humans, as well as how scientists came to learn what we know now, which is told in the same clever and funny style that Bryson is known for)
 
 
 
 

3. The Silence of the Lambs, by Thomas Harris

What can I say about the greatest psychological thriller of all time? If you thought the movie was awesome, well, the book is even better. The book looks at the mindgames Hannibal Lecter plays on everyone in much greater detail, and has many interesting characters that get little or no attention in the movie. Be sure to check out my Hannibal Lecter fan page.
 
 

Also recommended by Thomas Harris: Red Dragon (another book that's even better than the awesome movie, though it reads somewhat like a rough draft for Silence of the Lambs)
 
 
 
 
 

4. Ender's Game, by Orson Scott Card

Anyone who likes military fiction, science fiction, or political thrillers has probably already read this series, but in case you haven't yet, get to it. Now. I'm not kidding. Enders game tells the story of a future Earth that was threatened by annhilation by aliens once already. Having barely escaped destruction the last time, humanity gets to work training military geniuses from a young age. These bright young people from all over the world face off against each other in a series of wargames designed to see who the best strategists are. The strategies that they come up with and the interactions between the children make for a fascinating read that was my favorite book of all time before Angels and Demons came along (and that only narrowly surpassed Ender's Game).
 
 

Also in the series (all highly recommended): Speaker for the Dead, Xenocide, Children of the Mind (these first three and Ender's game follow Peter "Ender" Wiggin), Ender's Shadow, Shadow of the Hegemon, Shadow Puppets (these last three follow Ender's friend Bean and older brother, who were relatively minor characters in the first books in  the series).
 
 
 
 
 

5. Hitchhiker's Guide to the Galaxy by Douglas Adams

This series is essentially Monty Python's Flying Circus in space. Douglas Adams is a master of British humor, and this book tells of a universe  without logic, where everything we assumed is wrong, and was replaced with something more random and just all around wacky.  If you haven't read this yet, there's something wrong with you. 42.
 
 

Also in this series (all highly recommended, and available in an Omnibus edition): The Restaurant at the End of the Universe, Life the Universe and Everything, So Long and Thanks for all the Fish, Young Zaphod Plays it safe, and Mostly Harmless.