Hi starburst92,
Sorry for the delay in responding. As the makers of the exam, I'm obviously going to recommend our Official Guide for GMAT Review!
If you'd prefer to do a little research and see what books other test takers are recommending, I'd suggest you check out two blogs: Beat the GMAT and GMAT Club, you'll be able to get advice from people have are about to take the GMAT, those who have already taken it and test prep tutors.
A product I would definitely recommend you get from mba.com, which is the official site for the GMAT, is our free GMAT Prep software. The software includes 90 free questions – 30 Quantitative, 45 Verbal, 15 Integrated Reasoning – with answers and explanations and 2 full-length computer adaptive practice GMAT exams:
http://www.mba.com/global/store/store-catalog/gmat-preparation/free-gmatprep-software.aspxIn terms of the amount of time to dedicate to studying, it various from person to person. According to our research, GMAT test takers who achieve scores between 600-700 report having undertaken an average of 90 to 100 hours of preparation. The prep software should give you a good indication of how long you need to prepare.
I would recommend that you shortlist the top 3 or 4 schools you're interested in and see what average or score range they publish.
I hope this information has been useful. if you have any other questions about the exam, feel free to email me or visit mba.com for more information.
Thanks,
Tina