Larry Krieger has written a nice crash course that you can find on amazon. I read it all the night before the AP, took 8 hours, and I got a 5. However I also had the best teacher in America and could've scored a 5 without any review..
But anyways. Read that book a ton of times. It literally has the answers to every question. It's almost uncanny. I also recommend you read other stuff just to get the hang of it first.. but I seriously think that if you read his book at least 3 times, you can at least get a 3 or 4..