If you haven't already, you should get your student pilot certificate and airman medical. Based on your original post, since you said you're starting next week, it looks like you've already picked a school, so my suggestion would be to ask around for suggestions for a good aviation medical examiner (AME). Another option would be to ask on these forums for suggestions for a good AME around your location. You could also search the FAA database here:
http://www.faa.gov/pilots/amelocator/index.cfm
You'll definitely want to buy a headset. Your school or instructor may be able to provide one, but that's not something you'll always be able to depend on. I've personally been using the same DC 10-13.4 headset since I first started flying, and I like it. But if you have money to spend, you may want to try on a few headsets (including some of the pricier models) to see which fits best on you.
For written preparation, I used the Gleim test prep books. The website
http://www.exams4pilots.com/ is also quite helpful. They worked well for me (never scored lower than 96% on a written, and I've taken about 8!). The actual written materials you use may depend to some degree on the preferences of your flight school or instructor. Ask whoever you'll be flying with if he or she has any suggestions.
You'll also want a copy of the latest FAR/AIM. I've always used ASA's version, though they're all pretty much the same. You may also want to find out exactly what model and year airplane you'll be flying so you can pick up a pilot operating handbook (POH) for it. As a general rule, it's good for a student to have the airplane and its systems memorized through and through before they solo... so you might as well get a head start!
If you're looking for a dedicated ground school, you may want to look around at some local county colleges. They often will provide ground school classes at a pretty reasonable price. If you do choose to attend ground school, they'll set their own requirements for what books you use. If not, I've always found jeppesen's private pilot manual to be fairly good.
Another book that I'd highly, highly recommend is Wolfgang Langewiesche's "Stick & Rudder." It's on my unwritten list of "required reading" for private pilots.
Good luck! Learning to fly is a lot of work, but it's absolutely worth the effort!