I've heard good words for this book, see pic.
For other basic introductions, you won't go far wrong with the Wikipedia and Rational Wiki entries.
On the fiction side, two classics would be: The Crying of Lot 49 and Slaughterhouse-Five. The key here is to recognize both Pynchon and Vonnegut are not writing bizarre tales merely for the sake of doing so. In very tangible ways they are trying to better illustrate reality.
Postmodernism tends to place a great deal of emphasis on the nature of people and society over other considerations. It's an artistic form, and mode of thought, that has much to teach us. However, as with any system, it can be inartfully applied. Those "other considerations" are not always made more amendable via a slapdash postmodern whitewash. Science being one such.
A good postmodern fictional treatment of science can be found from none other than Isaac Asimov. The Gods Themselves is an excellent demonstration of how science may fail as a system. The key here is in how people act, react, and interact. Plus, what does it mean to be "right" about reality? Asimov's novel is not ranked high on the postmodern fiction list probably due to his usual clarity. The nature of what is going on, and why, is rendered crystal clear. If nothing else, this demonstrates an obscurity in form is no requirement to postmodern fiction writing.
On the philosophical side, I won't make any recommendations. I only note how an army of graduate students have been wailing away on Lacan, et. al., for decades. It isn't really necessary to wallow through the original source material. You'll go farther and faster with learned summaries and basic works of explanatory analysis of their ideas. But, again, I'll leave recommendations of such for others.
