1984 is classic, If you haven't read it yet, I recommend picking up a copy. It's only 5 or 6 bucks, and you should be happy with the purchase.
For me it took a bit to get into at first but after a little bit I just flew through it.
The similarities between our current society and Orwell's fictional society are strikingly similar, enough to make you think that that world could be just around the corner. :|
Another good book I need to re-read is Good Omens, I'll let you look it up and make the decision for yourselves, but if you like dark humor involving Angels and Devils and the end of the world, this book is for you.
Here is a link to the Amazon.com page for Good Omens.