The easiest way to find used books:  Advanced Book Exchange .   Tell the system what you want and it will search thousands of book dealers for it every day and e-mail the results to you.  Unfortunately in the last year prices have skyrocketed as dealers compare prices and all try to raise the stakes.

Other resources:

• Bookfinder.com
• Alibris

My Tom Swift Jr. book collection still needs #30, #31, and #33 "Galaxy Ghosts".
Also looking for Bertrand Brinley's "The Big Kerplop" and "Apollo:The Race to the Moon" by Murray and Cox..

Books that changed my life:

• Atlas Shrugged - Ayn Rand:  Most of what you've been taught about how to think and what to value are bass-ackwards.
• Illusions: The Adventures of a Reluctant Messiah - Richard Bach: Very inspirational.  Great quotes.
• The Mad Scientist's Club - Bertrand Brinley: My bible as a youngster.  Even formed a science club SOBCA, which has now been resurrected as STAC.
• The Six Pillars of Self-Esteem - Nathaniel Branden: The instruction manual for your brain.  This should be required reading in school and teachers should have to pass a class based on this before being certified.
• Systemantics - John Gall: Everything is connected to everything else, so it is very useful to undersand how these systems work, and fail.  Very humorous and filled with truths so clear they ring like bells.  Systems are created to serve purposes, but the primary goal immediately becomes the preservation and growth of the system: i.e. H.U.D., TVA, (insert your favorite agency acronym)
• Zen and the Art of Motorcycle Maintenance - Robert M Pirsig: My introduction to interleaved story lines, philosophy, and "quality".
• Johnathan Livingston Seagull - Richard Bach: Never be afraid to be an individual.  Pursue your dreams regardless of the costs.
• 1966 Estes Model Rocket Catalog: Rocketry was my first hobby.  This catalog has been read cover to cover hundreds of times.
• 1954 Boy Scout Handbook - (my father's) Showed how to really survive under difficult circumstances.  All kinds of interesting skills and projects they don't teach anymore.

• Apollo: The Behind the Scenes Story of America's Race to the Moon: Murray & Cox: Geeks rule!
• The Ayn Rand Lexicon - Harry Binswanger: A great glossary of philosophical terminology using excerpts of Ayn Rands works to define each term.
• The Rocket Boys - Homer Hickam: Just a great story.  My father and uncles had a similar club in the early sixties.  They launched 6' tall steel pipe rockets over a mile up.  One had a mouse passenger but it didn't survive the g-forces.
• Principles of Dynamic Systems - Jay Forrester: The techniques for understanding, modeling, and building simple or complex systems.  Great explaination of how toilets work.
• Fate is the Hunter (+others)- Ernest K Gann: (esp Hostage to Fortune, Gentleman of Adventure)
• The Hitchhiker's Guide to the Galaxy (5 book trillogy)- Douglas Adams:  Don't Panic!  I have my towel.
• Without Remorse  (+ others)- Tom Clancy: This was the only story of his with moral dilema.  But all have great technical detail and multi-threaded story lines.
• Flight of the Intruder (+ others)- Stephen Coontz: Just great story telling with the incredible technical detail of someone who'd been there.
• Flight of the Old Dog (+ others)- Dale Brown
• Fulcrum - Alexander Zuyev: the story of the Russian pilot who defected with a MiG-29 (I met him) - "Screw the KGB!"
• Andromeda Strain: Michael Creighton: Saw the movie first as a child - pretty scary.
• Collosus (trillogy) - D. F. Jones
• The Cuckoo's Egg - Clifford Stoll: How an astrophysicist tracked down an international hacker.  Amazing application of scientific lab equipment toward data filtering challenges.
• Thud Ridge - Col. Jack Broughton:  One of the best Vietnam aviation autobiographies.
• Engineer's Notebook - Forrest Mimms:  My inspiration for many electronics projects.
• Surely You're Joking Dr. Feynman - Richard P. Feynman: It's the unusual people who are interesting.
• Nine Princes in Amber - Roger Zalazny:  The only Science Fantasy I've liked.  A non-techno precursor to The Matrix. A man wakes up in a hospital with no idea of who he is.  The answer turns out to be quite interesting.
• Tom Swift Jr. (series) - Victor Appleton (pseudonm): My father gave me three books from his childhood.  The collection of the remaining ones became an obsession.  I still need #30,31,33.
• How and Why Wonder Books (Science & Technology series): My mother is a very good teacher.  Starting at about age three we'd get a new book each month and do most of the experiments.   Thanks to her, I built a great foundation of knowledge in a wide variety of subjects well before starting public school.  Of course my father helped to: one of my first toys was a simple board with a transformer, buzzer, doorbell button, and some loose wires for me to learn how to wire up circuits.  (Not all toys were technical, my other favorite childhood toy was my BB gun).

• Air & Space Smithsonian
• Popular Science
• Circuit Cellar
• Nuts & Volts
• Extreme Rocketry