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See my earlier comments recommending "The Crying of Lot 49" by Pynchon to follow the Post Office theme.
If you haven't read Neal Stephenson, start with "Snow Crash."
If you can find some John Varley, any Varley, do it. Along this end of the world theme, try "Slow Apocalypse." His short stories are great.
For an examination of conspiracy theories (also topical!) Umberto Eco's "Foucault's Pendulum" is a must -but long - read.