I love first-contact stories; they so clearly delineate who we are as a species by contrasting us with a completely unknowable version of society. Lem, a Polish writer best known for the heady and difficult Solaris, invests his with humor and humanity as Earth scientists struggle to decode a mysterious message from outer space. There's plenty of infighting among the group, and Lem treats us to their various arguments on scientific ethics, epistemology, and the nature of God. Action-packed this book is not, but if you're interested in the nature of humanity, there are few better places to search than this masterpiece.
Dick, acknowledged master of the psychedelic sci-fi tale, has his trippy masterpiece in Ubik, a twisty tale set in the then-far-flung future of 1992. Technological and evolutionary advances have released the populace's psychic powers, challenging individual privacy and creating a whole new world of espionage, while cryogenic freezing allows more and more people to live "half-lives," telepathically advanced states of being caught between life and death. As the plot progresses, our protagonists are caught in double cross after double cross until they face the ultimate question: Are we alive, or are we dead?