GiMeSpace Bootstrapped dropdown menu for Joomla®supports multi level dropdowns and multicolumn dropdown on level 2. (See examples on top of this page)
This module will add the required code making a menu show correctly with twitter bootstrap since the standard menu in Joomla® 3.x is still not doing this...
For having multiple columns you need to enable this in the module and have separator menu items in you submenu where you want to split the menu to the next column.
download version 1.0 here for free!
GiMeSpace is making freeware and shareware utilities for windows desktop users. Click for the main site here!