Quartz Icon Set is a collection of 90 simple but stylish icons that are in 64*64px size & PNG format.
The set contains icons from “files/folders” to main website objects like “search, home, download” or social bookmarking ones.
They are free to use in both personal 6 commercial projects.
P.S. Thanks very much to Andy Gongea, the designer of the set, for the suggestion. And, the set is also shared on his website.