I have released a new module, "Popups: Add and Reference":http://drupal.org/project/popups_reference, which solves a problem that has been bugging me for years: creating a reference to a node that does not yet exist. The module 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 module":http://drupal.org/project/popups.
My initial inspiration was the 4.7 module "Add and Reference":http://drupal.org/project/add_n_reference by tema, which I found out about in the g.d.o thead "Current best solution for add and reference?":http://groups.drupal.org/node/13162
I am hoping to do more modules like this, which show off the flexibility and power of the in-page popup UI.