princeton review is a good sat prep course. i imagine the high school offers good materials and probably a review class. ours did but that was 20 years ago.
Read as many books (any books) as possible. Do crossword puzzles. Do logic problems.
Get help with the math if necessary, but just exposing him to the wordplay used in crosswords, as well as the utility of constant reading will raise his verbal score significantly.
Are you still looking? The official book put out by the College Board has 10 practice tests in it. Get this book and go through all the practice tests; that will help a lot. I also do private SAT tutoring...contact me if interested.