I've tried the whole gambit of DAT Prep materials and they're great until you hit something you don't understand. I agree with klutzy1987 about finding a good review course.
You might consider the UMKC School of Dentistry DAT Prep Course. It's being taught by actual professors. They give you the Topscore CD and apparently you get handouts/notes from the professors as well. It's a 1/3 the price of Kaplan and it's done online and it's live so you can ask questions.
The course is delivered by CE Webinar.
http://www.cewebinar.com. I'm doing the March session.