Free Line Icons
48 icons inside, fully scalable vector shape icons. Available in PNG, EPS, PDF format.
Free Line Icons is a free Icon design resource made by Dribbble user Arun. 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.