Font Awesome gives you scalable vector icons that can instantly be customized — size, color, drop shadow, and anything that can be done with the power of CSS.

You can access the complete set of 500+ icons in Font Awesome at the following link:
Font Awesome website

Changelog
Font Awesome has been updated to the latest released version: 4.4.0

Visio comes with another great font icon library: Ionicons. We found it very helpful and it comes with lots of new icons that you will simply love.

You can access the Ionicons font library at the following link:
Ionicons website