Font Awesomes icons have now become the standard in web template development with Bootstrap. We have used them on Wordpress and Joomla template frameworks. Their implementations vary slightly, but in the end, 'icon-CLASS_NAME' in <span> delivers the goodies.
The icon set is found here: http://fortawesome.github.io/Font-Awesome/icons/
What we found very useful is the site has organized the icons in groups saving us a lot of time. Many template providers documentation do not have this.
We also found a site that gives the CSS content values for each icon - this allows you to insert the icons through CSS rules: http://astronautweb.co/snippet/font-awesome/
The only downside? There isn't an icon for fax, yet...