To be honest, NDAs (non-disclosure agreements) aren’t very useful in very early stages in the startup life-cycle. If you require an NDA from someone who you are about to pitch your idea to, they typically won’t sign it. Why not? Read Brad Feld and Mike Lincoln.
However, when discussing patent applications, partnerships, joint ventures, mergers, acquisitions etc., NDAs can come in handy.
I have created two versions of NDAs. One is one-way/unilateral (e.g. when you give sensitive blueprints to a supplier) and the other one is two-way/mutual (e.g. when discussing a merger and confidential information will flow both ways).