What are some drupal 7 mega menus that allows view blocks to be inserted?
You can use Menu Attach Block module to render block as menu.




  Menu Attach Block allows you to attach blocks to standard core Drupal
  menu items. This is especially useful for creating complex dropdown
  menus and mega menus.
  
  Any block can be used, including blocks generated by other modules.
  Blocks generated by Views are particularly good candidates for
  embedding.