For Organic Chemistry, I would work primarily with Chad's videos over at course saver, google it, and use these Ochem as a second language I&II (~$15-30 each) books:
http://www.amazon.com/Organic-Chemi...=sr_1_1?s=books&ie=UTF8&qid=1298891137&sr=1-1
For Biology I would use Barron's AP biology (~$10), and if possible get Campbell's biology textbook as a reference (or you can ask questions on SDN as many of us have Campbells and will surely help you):
http://www.amazon.com/Barrons-Biolo...0515/ref=sr_1_1?ie=UTF8&qid=1298891085&sr=8-1
General Chemistry, also use Chad's videos, and a textbook, though Princeton's AP chem book is supposedly good as well.
For QR, use Khan Academy (free), he covers just about everything you could see on the DAT.
http://www.khanacademy.org/
Use Crack DAT PAT ($100+):
http://crackdat.com/
There are additional resources that will reinforce everything you study for, and can also be used for subjects you already know well, these include DAT Destroyer+Math Destroyer ($200), Freelance Teacher (free, additional video resource covering gen chem and ochem), as well as various practice tests.
I encourage you to look in SDN's for sale area for many of these products at discount prices:
http://forums.studentdoctor.net/forumdisplay.php?f=230
Destroyer:
http://www.orgoman.com/products.html
Freelance Teacher:
http://www.freelance-teacher.com/videos.htm
I personally do not believe Kaplan's Blue Book is necessary, though I cannot deny that I do own it and have used it. When I purchased it, I believed it was a all-in-one book for the DAT, that I wouldn't need anything else. This may be true if you know your subjects very well or you are not shooting for the best score possible, but otherwise I do not condone it as a standalone. With that said, I think just about everything it has to offer can be covered by the other resources listed here individually (but better than KBB overall).
Any further questions, shoot. Best of luck with your studies.
Cheers