Free Download: Retina UI Web Kit

This fantastic UI kit was created by Bradley Bussolini. It is optimized for high resolution screens with Retina quality elements. The zip folder contains two files, one with UI elements and another for a sample page mock. Both files are in Photoshop PSD format. 

It's free to use for both personal and commercial purposes, however, the files themselves cannot be redistributed.

See Bradley's portfolio on Behance.