Snow Crash - Already mentioned
Takeshi Kovacs series (Woken Furies, et al) - Interesting take on immortality where your entire mind is in a stack of silicon and can be freely swapped to other bodies. For example, they have faster than light communication but not travel, so instead of traveling from one planet to another, they simply download your consciousness into a new body.
Forever War - A war that takes place over centuries due to lack of faster-than-light space travel, and how Earth changes every time the protagonist come back from a fight.
Honor Harrington series - Already mentioned
Cryptonomicon - Already mentioned
Mars seris - Already mentioned
Jupiter - Nice book about politics of discovering an alien race, enclosed space pshycology
Starfist Series - Already mentioned
Warhammer 40k - Already mentioned
Footfall - Some near-future hard core sci-fi as to what would happen if we were invaded
Prince Roger series (March Upcountry, etc) - Popcorn sci-fi really, but the main character goes through a significant change through the books. It has a bit more of a draw due to heavy focus on said character and his personality changes/"growing up".
Tau Zero - Bunch of colonists traveling in an enclosed ship at near the speed of light can't slow down when they need to, so millions of years pass in the normal universe while they slingshot out of the galaxy. Big on psychological interpersonal relationships.