Responsive Wireframes - high-level example of how a page reflows according to screen size. Example is a typical ecommerce site.
Flat UI Pack for Apps - Build Apps. Beautifully by Rebirth Pixel, via Behance
Vanilla UI Kit
Mueller Grid System website
Tour and Travel Icons - Business Icons
Portfolio App Design Ui Kit Psd http://www.blugraphic.com/
iPhone and iPhone 4 Grid Systems