Freebbble!

(Sorry for the heavy-to-load GIF). AI vector format. Full version is paid only.

UI8 Wireframe Kit (Lite version) is a free Template design resource made by Dribbble user Dash. 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.