This module is seeking a new maintainer.
Popups: Add and Reference adds a link to CCK's Node Reference widget that makes it easy to add a new node without having to leave the edit page. It is built on top of my Popups API module: http://drupal.org/project/popups
Initial inspiration: Add and Reference by tema: http://drupal.org/project/add_n_reference
Not everything that would normally go on a node creation page works in a popup. In particular WYSIWYG editors like TinyMCE do not work. If you would be interested in funding an effort to get wysiwygs working inside popups, drop me a line.