I have a list somewhere that my teacher gave me last year of all the novels that have appeared on the AP tests in the last however many years, listed with what year they appeared. If you'd like, I could find that and scan it in to email it to you. I've looked for the same list online, but I can't find it. Well, and I think that's more important for AP Literature than Language.
In my AP class (I was in Lit, but the Language class had mostly the same reading list) we read:
As I lay Dying by William Faulkner
1984 by George Orwell (that's an important one)
The Language classes also read Brave New World by Aldous Huxley
Hamlet (I personally watched the 4-hour, word-for-word movie version, and read it in subtitles. It counts!)
Rosencrantz and Guildenstern are Dead by Tom Stoppard and
The Stranger by Albert Camus (to be familiar with absurdism)
I can't remember the rest, out of hand. If I think of any, I'll add them here.
To Kill a Mockingbird by Harper Lee and The Scarlet Letter by Hawthorne are good ones for good basic themes you can draw on if you need to.
For the last of the free response questions on the test, you might need to read or be familiar with some basic philosophy and ethics, too. This last year's question was about the ethics of offering material incentives for charity. You're supposed to draw examples to support your argument from your reading or experience. I used Ayn Rand's ethics, because that was all I could call to mind that was relevant, but generally higher education frowns upon Ayn Rand. I do recommend her, though. Atlas Shrugged or The Fountainhead by Ayn Rand are good for an interesting and different perspective on ethics, if you've ever need of one.
Good luck!