Looking for a good nav plugin

I was curious if anyone had a good recommendation for a responsive menu for WPMU with a developer license?

In our custom development it would be nice to have a solid menu that is developed well and not likely to fade away.

We really like http://wpmegamenu.com/ but this menu has to be acquired one license at a time.

Characteristics we would like:
Multiple style
Horizontal and vertical options
Ability to insert bg images for buttons or add images.
Mega Menu

Any recommendations are appreciated. Flexibility is huge. For Joomla we use swmenupro.