Codrops has written a tutorial: Circle Hover Effects with CSS Transitions, about how to create different interesting hover effects on circles with CSS transitions and 3D rotations.

Since we have the border radius property, we can create circular shapes and they have been appearing more often as design elements in websites. Sometimes, we do enjoy seeing is the circular thumbnail which just looks so much more interesting than the usual rectangular. And it is because the circle is such a special shape, we are going to create some special hover effects for it.

Requirements: CSS3
Demo: http://tympanus.net/Tutorials/CircleHoverEffects/
License: License Free