I'm aware of:
- Subform - http://drupal.org/project/subform - 4.7
- Add and Reference - http://drupal.org/project/add_n_reference - 4.7
- Addnode - http://drupal.org/project/addnode - 5.x
- Noderefferer Create - http://drupal.org/project/nodereferrer_create - 6.x available, depends on nodereferrer which doesn't seem to have 6.x available?
Addnode and Nodereferrer look like the leading candidates, and assuming that NR is going to be available for D6 soon, I'd use that. BUT, creating items on the same form page as Addnode does seems the most elegant.
Have people had experience with this, and any info on availability / suitability for D6?
