‘Flatty Shadow’ is an interactive One Pager by Deepak Reddy where you can actually tweak the design on a flat icon set. By tweak I mean change the color, shadow angle and shadow depth on the icons. Very useful, cheers Deepak!
This website has unfortunately been redesigned or gone offline, so I have removed the direct link to it. The screenshot below hopefully preserved enough of the design but if you are really keen to inspect further, try this Archive.org link. FYI: the site was first featured on 21 November 2014.