Valis
Supposedly semi-autobiographical, this book can be "hard going" in places - PKD mixes religion, mythology and extraterrestrial intervention with events in his personal life from 1974 onwards. This book made me laugh out loud, scratch my head in bewilderment and gave my vocabulary a thorough going over.
If you've never read a PKD book before make sure you leave this one until later or it might just put you off trying one of his more (un)conventional novels.
Just started "Brave New World" by Aldous Huxley then I'll move onto PKD's "A Scanner Darkly" and finally revel in my second outing with Orwell's "Nineteen Eighty Four".
We each live in our own realities - who's maintaining yours?
The only thing that you can be 100% sure of, is that you can't be 100% sure of anything.