Some of the most recommended materials on SDN are DAT Destroyer, Schaum's Bio and Campbell's Bio, Kaplan course materials, TopScore and Achiever practice tests. Barron's DAT book is good for some of the sections.
Kaplan's course is good if you need something to keep you on a schedule. Otherwise, find the Kaplan materials from somebody and save the extra money.
I'm selling all of my DAT books, tests, etc. Check out my ad - the link is in my signature - and feel free to PM me if you'd like more info.