Flat Icons has an impressive library of elements: lots of 2D, 3D and animated icons. Some icons are very specific and are rare to find, each icon is customizable.
You can download the icons to your PC or use the web app or software plug-in - wherever you are, they're easy to access.
In my job as a website builder and graphic designer I mostly need multiple icons of the same color for a single project. Ultimately, very useful and perfect for a quick job.