If you like Font Awesome, you're going to love Black Tie!
             

fa-underline · Unicode: f0cd · Created: v2.0 · Categories: Text Editor Icons

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

fa-underline
<i class="fa fa-underline"></i> fa-underline

Looking for more? Check out the examples.