Many are just classics (and not mindfuck in my opinion).

Hesse is good in general.

Kafka is good in a weird fucked up way and to be recommended after one had to deal with the legal system for example.

Castaneda is interesting fantasy, but many took it literal and a real cult evolved around his books (with him included as the Guru).

Peter Caroll is interesting, if you like the occult.

And Robert Anton Wilsons Illuminatus! is the bible of conspiracy theories.

(But a really good book and deserving of the mindfuck category, I think it popularized the term mindfuck)

The Trial does deserve the term mindfuck, I think, both because of the story and because it upends the notion of what most people expect of a novel. Kafka's other words are weird and wonderful and not nearly as hard to read as some seem to think, but if you've read The Trial, they're not very mindfuck-y, and that's a big problem with a list like this - each book you read that is still a mindfuck will make a lot of the rest seem pretty pedestrian (though often still good).