Drupal Module Corresponding node reference
Cnr syncs the node reference between two node types which have a nodereference to each other, so double editing nodes is no more needed. If one node has a reference the other node receives also a reference to the saved node if it is referenced in that node.
Drupal.org project page : http://drupal.org/project/cnr
Drupalmodules.com : http://drupalmodules.com/module/corresponding-node-references