80 Thin Icons PSD
From the author: “These are free to use anyway you like (you may not redistribute or sell these icons on any other website). If you use here on your dribble shot let me know so I can see what you’ve done.”
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.