Sometimes online prep might not be enough. The test is paper-based after all, so you should get some prep in with the good old paper and pencil.
In my opinion, most of these books won't make the difference for you. Ultimately it's your dedication and hard work.
If I had to pick one book, it'd be the Princeton Review practice tests book. To me, and many people I've spoken with, it gives you questions that are slightly harder than what's ultimately on the SAT. When you get to the SAT, the real questions seem a lot easier.
This is the book I used to prepare for the test, before INeedAPencil.com of course!
