Buttons is one of a css library. It is built with Sass & Compass. It have very good collection of Buttons and their shapes including Flat Buttons, Icon Buttons, Glow Buttons, Rounded Buttons, Pill Buttons, Square Buttons, Circle Buttons, Block Buttons, wrapper buttons, Form Elements and many more collections.

CSS Button Library
CSS Button Library

Website: http://alexwolfe.github.io/Buttons
Download Source: https://github.com/alexwolfe/Buttons