George Orwell's, "Nineteen Eighty-Four" certainly opened my eyes wider than they already were. I only read it a few years ago and even though I was aware of the basic story and premise beforehand (the phrase 'Big Brother' and what that terrifying idea embodies is now ubiquitous), it didn't really prepare me for the literary hammer-blow that is the book itself. To describe it as profound, insightful and relevant is no exaggeration. Almost as frightening as the dystopian future it describes is the explanation of 'Newspeak' which is included as an appendix. The idea of manipulating language to such a degree that it changes the very nature of thought is probably more relevant today than it's ever been:
http://goo.gl/rrUn
I wouldn't say that the book changed my life but I would say that it brought certain contemporary issues into sharper focus. In that regard, I would say that it has had a very positive influence on my life. If I ever read a more cogent description of how to manipulate people, I will be astonished.