Font Awesome
             

fa-folder-open-o · Unicode: f115 · Created: v3.0 · Categories: Web Application Icons

After you get up and running, you can place Font Awesome icons just about anywhere with the <i> tag:

fa-folder-open-o 
<i class="fa fa-folder-open-o"></i> fa-folder-open-o

Looking for more? Check out the examples.