I agree with Anon, Atlas Shrugged is a great read (whether or not you agree with the author's particular philosophical leanings). His Dark Materials series (Northern Lights, The Subtle Knife, and The Amber Spyglass) by Phillip Pullman is probably the best story I have ever read. Those books changed my life. If you would be into religious themed sci-fi The Sparrow is a really good read, but be warned it is kind of like the movie "Requiem For a Dream" in that it is fucking harrowing and will leave you shocked and horrified. Also, I just finished How to Live Safely in a Science Fictional Universe, and I loved that book. Not even really THAT science-fictiony, more like philosophical time based wordplay. But fun.