Cosmic Trigger 1 by Robert Anton Wilson
Robert Anton Wilson is one of the best writers out there in my opinion. Being described by Dr Richard Bandler as the 'most intelligent person on the planet' Wilson writes the kind of books that can surprise you, shock you, inspire you and move you.
Written in the form of short chapters which go in different directions but all seem to coherently explain his brilliant insights into life and the world, this is another example of the kind of book from Wilson that makes you more intelligent.
By opening up your perceptions, challenging you and teaching you how to see the same things from mulpile points of view this book sets the standard continued in the two sequels.
Put simply, if you aren't a fan yet... become one... it can only help your mind.