
Valis is about a schizophrenic hero named Horselover Fat; the hidden mysteries of Gnostic Christianity; and reality as revealed through a pink laser. This is a theological detective story, in which God is both a missing person and the perpetrator of the ultimate crime.
If you want the intellectual take go with A Canticle for Leibowitz (Miller), Oryx and Crake (Atwood) or Solaris (Lem).
If you want the 60s hard-science rooted societal outlook from an ex-Naval Engineer with strong views on gender roles, it's all about Heinlein - Stranger in a Strange Land, The Moon is a Harsh Mistress, Starship Troopers etc..
If you want something to share with the young adults in your life, or simply some of the finest writing in the contemporary British YA canon, then Philip Pulman's magnificent homage to 'Paradise Lost' - the 'His Dark Materials trilogy' - cannot come more highly recommended. Usually categorised as 'fantasy', and heavily indebted to Milton and Blake, this represents a master-class in parallel-universe world building with its own take on a Steampunk Oxford and a number of other science fiction tropes.
VALIS, Philip K Dick
Zen and the Art of Motorcycle Maintenance + also Lila, Robert Pirsig
Naked Lunch, William Burroughs
Immortality, Milan Kundera
Catch-22, Joseph Heller (pair with The Deserters, Charles Glass -- In fact a lot of the stuff in Catch-22 is actually toned down from reality)
Mastering the Core Teachings of Buddha, Daniel Ingram (but ignore 80% of it)