Module for putting blocks in menus
Sure; these are called 'megamenus' or 'meganavs' and there is a module directly for this: the Megamenu module.


  Mega menus are a type of drop-down, which seeks to overcome some of the usability drawbacks to traditional style drop-downs. Primarily, mega menus have two advantages:
  
  
  The information architecture of your navigation is made clearer and is visible all at once
  The amount of clicking, searching, and navigating is reduced
  
  
  This module allows you to build mega menus by leveraging jQuery and the existing Drupal menu system. Megamenu takes a Drupal menu that is 3 levels deep, and converts it into a categorized 3-level mega menu, which is placed into your site as a block.


The 7.2-x branch allows "embeded blocks within mega menus"