Seems most of the books recommended are for non-fiction, so I'll add some fiction to the mix.
The Hyperion Cantos series by Dan Simmons. It is deeply philosophical and caused me to think about life in a way no other science fiction has before or since. I found myself really sympathizing with the characters in these books, and found the overall plot incredibly fascinating.
Another good one is the Commonwealth Saga series (and others set in the same universe) by Peter F. Hamilton. It's a very _big_ space opera with lots of engaging characters, interesting technology, exciting descriptions of interstellar war, and a good reminder of just how unlike humanity an alien species could be. It really opened my mind to possibilities of humanity in the future in terms of how we might progress, both in terms of progressing out into the galaxy and how we could progress as a species.
The Hyperion Cantos series by Dan Simmons. It is deeply philosophical and caused me to think about life in a way no other science fiction has before or since. I found myself really sympathizing with the characters in these books, and found the overall plot incredibly fascinating.
Another good one is the Commonwealth Saga series (and others set in the same universe) by Peter F. Hamilton. It's a very _big_ space opera with lots of engaging characters, interesting technology, exciting descriptions of interstellar war, and a good reminder of just how unlike humanity an alien species could be. It really opened my mind to possibilities of humanity in the future in terms of how we might progress, both in terms of progressing out into the galaxy and how we could progress as a species.