It's tempting to just tell you to go away and read anything by Philip K. Dick that you can lay your hands on. You won't regret it. But here's a few you should definitely check out.
Do Androids Dream of Electric Sheep is the novel that Blade Runner was based on, but there's an awful lot in the novel that didn't make it into the film. It's set after World War Terminus, when radiation poisoning has killed most animals, so owning a live animal is a major social status, and most people cheat with robots that are indistinguishable from the real thing. But there are robots that are indistinguishable from humans, too, and they are making their way back to Earth where it is bounty hunter Rick Deckard's job to eliminate them.
Ubik concerns a group of psychics trapped in an explosion on the moon who consequently find themselves imprisoned in a fake reality that resembles 1930s America.
A Scanner Darkly was, Dick considered, his best novel. It tells the story of an undercover narcotics agent whose own mind is damaged by the drug he is investigating, so that he ends up investigating himself.
If you are intrigued by the alternate history of The Man in the High Castle
, then there are a host of great works you need to know about. For a start there's Pavane
by Keith Roberts, in which the Spanish Armada successfully invaded England and now, in the 1960s, it is a backward country held back by the power of the Church, a country in which highwaymen attack road trains, in which there are still fairies in the countryside, and in which the Inquisition still tortures any dissenters.