Vonnegut is king of good funny reads that move the mind, some favourites are Galapagos, Breakfast of Champions, and Cat's Cradle.

Philip K Dick is less fluffy about his mind-moving but wrote some corkers, the ones that have interested me most are VALIS, The 3 Stigmata of Palmer Eldritch and The Transmigration of Timothy Archer. There's some great stuff about minds and meaning-seeking and madness and reason.

The book I'd probably recommend above all others is Riddley Walker by Russel Hoban, it can be a bit of a hard start as it's not written in standard English - it's set in a future Kent hundreds (thousands?) of years after the collapse of a great modern civilisation. It's a story about humans, how meaning passes on through time, stories and where they come from, where they take us.

Really enjoying the Earthsea books by Ursula LeGuin just now - wizards, dragons etc. but it's about life and death and The Balance and human lives and all that good stuff. Epic but personal.

Also that reminds me of Shikasta by Doris Lessing and the other books associated, some big scale stuff but such insight into people and really moving.