I hear Campbell's Biology and Chemistry the Central Science are on some ADA suggested reading list that I haven't been able to find... Those might be good. Honestly, don't freak out about it. I would just take several practice tests and see where you're weak. One thing I will tell you is that, in my case at least, the DAT is not about depth, it's about breadth. The questions aren't "hard", but they pull things out that make you think "I would have never thought to study that..." So study anything you can get your hands on, don't rule anything out. The difference between a 19 and a 25 isn't memorizing the specifics of basic concepts in my opinion, it's having a broad knowledge of random things. Sorry it's not exactly a straight answer, but I hope this helped and good luck!