Hi Loveless (or is it Heartless?),
The most important book is The Official SAT Study Guide (aka the Blue Book) from the College Board. This is the only book with real test questions.
Personally I am a fan of PowerScore books---I know the author quite well ;). You can preview free chapters here: http://www.powerscore.com/sat/help/content_chapters.cfm. But there are many SAT prep books written by test prep companies. You can buy books that cover all three subject areas (math, reading, and writing), or books that cover each section separately and in more depth. Look for books that explain the content tested (such as right triangles) and then show you how that content may appear on the SAT. Make sure they have a lot of practice questions after each content section so that you can master each topic.
You can also find some good free test prep online. Sparknotes has a decent SAT review, although they omit some important concepts and add a few that are not tested on the SAT. They do not delve into the tricks of the test, but they offer a great review of the content that is required.
Vocabulary Flashcards: http://www.powerscore.com/sat/help/content_flashcards_vocab.cfm
Math and Writing Flashcards: http://www.powerscore.com/sat/help/content_flashcards.cfm
Free Book Chapters: http://www.powerscore.com/sat/help/content_chapters.cfm
Free Blue Book Database: http://www.powerscore.com/sat/help/content_bluebook.cfm
Free Content Review: http://www.sparknotes.com/testprep/newsat/
March 2005:
http://www.collegeboard.com/prod_downloads/prof/counselors/tests/sat/2007-08_sat_preparation_booklet.pdf
October 2005:
http://www.collegeboard.com/prod_downloads/sat/sat-preparation-booklet.pdf
January 2006:
http://www.collegeboard.com/prod_downloads/sat/sat-practice-test.pdf
To save money, visit your local library to see what they have in the way of test prep. They should have the Blue Book as well as some SAT prep books.
Good luck!