Number2.com - free test prep site with the ability to set up a "coaching relationship" with the student and a mentor such as a parent or anyone who will assist the student in staying on track with their study plan.
Vocabulary Builder and Math Notes - list of 5000 words with brief definitions and math notes.
College Board's practice site - contains a full SAT test for free, practice questions and study plan.
Fee-Based Test Prep
The Princeton Review - offers various options such as classroom and small group, on-line programs, and private tutoring.
Kaplan Test Prep - a variety of options and a variety of prices.