Today: The Stranger by Albert Camus.
The apparent simplicity of this novel belies the underlying complexity of its existentialist themes. It will take you approximately three hours to read, and quite possibly three months to fully understand. It's an excellent, excellent novel for people who are naturally analytic. I recommend that, should you choose to read the novel, you brush up on the basics of existentialism (specifically, absurdist existentialism) beforehand. Also, attack it with pencil and highlighter. Annotate it as if it were a poem.
I don't want to reveal any spoilers here (though you will find that the plot, in reality, is somewhat irrelevant in comparison to the overarching messages concerning the nature of humanity), but I promise that, should you take the time to analyze it, the richness of symbolism, metaphor, etc. will keep you both busy and extraordinarily satisfied.