What non-disclosure agreement do you use? Did you get it online? Would you be willing to share it for the world to use?
I have a sample NDA on the Resources Page of my website, http://www.fulmerlawfirm.com/?page_id=15 . Since I don't know your situation (and I'm not your attorney), I don't claim that it's necessarily appropriate for you, but it does cover the main things most people worry about.
Here are a few points that are commonly negotiated:
(1) The scope of confidential information. Is it limited to information related to a particular matter? Does it need to be marked as confidential?
(2) The duration of confidentiality. How long does it need to be confidential? How long do you have to disclose information that has to be confidential?
(3) How do you handle a company' affiliates -- can they see the information, or not? Can they provide confidential information? Who are the affiliates?
(4) Choice of law/venue
(5) Does the recipient have to return information at a certain time, or just upon request?
There are so many different variants of NDA's that most people have their lawyers craft one from a standard boiler plate. You can go to www.nolo.com and get one pretty cheap.
If you are looking around for one, there are a couple of things that should be in it. These include: