Earlier today I created a new sandbox module on Drupal.org called "Omega Responsive Menu," and although I have Omega in the title, it should be theme agnostic. The reason I called it Omega Responsive Menu is due to the fact I built it for all the Omega 3 sites I have had to work on.
So, what does it do? Drupal's theme function for the main menu tree will not provide and tiered link structure, only the top level of links. Kind of makes sub-menu navigation difficult. There are modules such as Superfish and Megamenu...but there's too much bloat and difficult for Drupal theme developers to work with (in my opinion.)
This new module provides a 3-tiered main menu alternative and the CSS/JS for sub menus. It also provides conversion into a responsive menu. On mobile devices it will add a menu toggle that slides up or down the main navigation.
Project info & examples: http://glamanate.com/omega-responsive-menu-module