I've been using couple of mega menu modules on drupal. While megamenu is under inactive developed (I couldn't get it work), the others such as menu minipanels, mucho menus... are complicated to new user like me, As far as I've been trying to test, Superfish works like a charm but it's limited in adding blocks to the menu. MD Mega Menu is nice too but I gotta pay for it. So our team decided to develop a new megamenu module at http://drupal.org/project/tb_megamenu. I believe you guys will find this module interesting, easy and highly flexible.