With the flat design trend on the rise at the moment, one thing that stands out is the use of long flat shadows, particularly for small UI elements and icons. These shadows have a characteristic 45 angle below the horizontal axis and a gradient color close to the background shade can be applied.
The Long shadow effect adds a great deal of depth while still retaining an essentially flat aesthetic.
jQuery Flat Shadow is a small jQuery plugin that will automatically cast a long flat shadow creating depth for your flat UI elements.