Icns Free PSD
From the author: “everything is vector and you can use it however you like. Just don’t sell them.”
Icns Free PSD is a free Icon design resource made by Dribbble user Gil. As far as I can tell, its license is Free for Commercial and Personal Purposes.
Helpful hint: Dribbble users are nice. If the license is unknown, it is usually because they forgot to mention it explicitly; not because they were being stingy. Ask nicely and they will probably allow you to use it.