What's aspects of sci-fi or fantasy draw you? I personally go for the weirder sci-fi that seemed to come out of the imaginative (and, well, drug-fueled, probably) 60's and 70's, so my recommendations tend to come from that.

Dune by Frank Herbert - I'll get the obvious one out of the way. Everyone needs to read at least the first book. The world-building is a commentary on our own and none of the movies, series or games will every really capture the books in their entirety. There is just so much more to Dune than the barely-below-the-surface treatments we get with film because they have to appeal to a mass audience that tends to have the relative intelligence of my left shoe.

Candy Man by Vincent King - take PKD's Electric Sheep question of what makes a human a human, then explore the answer in a far-flung future that ends up being a bit of a nightmare circus. Great world-building, here, but King reveals in slow morsels that leave us with questions and fuel turning the page. While his other works are not really that prolific, he hit the nail on the head with this one, bringing some dialect playfulness to the writing that just adds to the immersion. It's a haunting world, unsure of why it exists due to short memories and withholding of information, and unintentionally hints at the modern day disquiet of man as we race toward whatever Singularity we have accidentally or intentionally created.

Colossus by D. F. Jones - a bit like Wargames but more swanky, the US and Russia each create artificial super-intelligence then let them talk to each other, which goes about as well as you can imagine. The story hints at the notion that as soon as politics gets involved with science, things tend to get really cocked up, resulting in hostile takeovers, or worse, annihilation. It's a short read, and should be on the to-do list of anyone experiencing existential dread over the AI race today.

A Canticle For Leibowitz by Walter M. Miller - everyone needs a bit of post-apocalypsia now and then and I always recommend this one to get your fix. Here's an extreme treatment of what happens when anti-intellectualism becomes the modus operendi as we are thrust into a harsh and desolate world brought about by global nuclear war, roaming mobs blaming science (rather that politics, as Simpletons will do) for getting humanity into the mess it's in, going so far as to forbid pretty much any book-learning or education beyond the church. As artifacts from the past (our present, more or less) are uncovered, things get a bit hectic.

I'm also happy to take any recommendations, enjoying other authors like Stanislaw Lem, John Brunner, Robert Heinlein, Vonnegut, Jack Vance, etc. Reading books is probably one of the few things in my life that makes me feel a little less alone.