Well, I work for Kaplan, a test prep company based out of Washington DC (I think - we're a subsidiary of The Washington Post), so I can personally comment on their books. They have a good strategy and the books are put together quite well (though, then again, I am very familiar with them). I know that the few books I've seen from Princeton review are also good.
Basically, pick a reputable book, but be sure do the book (or at least read through the sections of the test you want to improve on). The greatest book in the world will fail to raise your grade if you never look through it.
Additionally, I know that the Kaplan books have practice tests in the back. Take those tests under game day conditions (properly timed, in a quiet, mostly annoyance-free zone). Also, be prepared to take the test more than once. The SAT is the first real marathon of a test you'll take in your life (and in most cases, the only one). It is 4 hours long and being mentally prepared to still do well on that last hour is key.
Take it a few times; it won't hurt you.
Feel free to shoot me a PM with any other, specific questions.