Chris Shattuck: How to use images for menu items in Drupal with a simple preprocessing function
This tutorial is sponsored by the Save Joseph campaign, a grassroots effort to find a good friend, stellar artist and all around amazing person a satisfying, creative job in the next 8 days. I know the Drupal community could use this kind of talent. Learn more about the effort at savejoseph.org. If you have any ideas on how I can get the word out about this, let me know!
My use case was that I wanted to be able to use social media icons for menu items so that we could re-arrage, add or remove items directly from the menu management interface:. The result is what you see below:

To use images for menu items in Drupal, the first step is to create an override theme function for theme_menu_item_link() in your theme's template.php file. The idea is to first run your image handling bit to switch out text for images, and then hand it over to the parent theme to do the rest. In my case, I'm using the Zen theme.