An appealing alternative to standard hard to navigate dropdown menus; options are shown in one large panel that allows for categorization, icons, etc. Article at Sitepoint: http://www.sitepoint.com/blogs/2009/03/30/mega-drop-down-menus/

Examples:

• http://www.actionenvelope.com/ 
• http://www.foodnetwork.com/
•  http://www.emc.com/support-training/index.htm

I suspect it would be a challenge to implement in Drupal, but not impossible.