I have created a module for a client which I am calling "ups_tracking_number" which is more or less a custom field type with three displays: text, link (links tracking number to UPS Web site) and detail.
The detail view is the most interesting, and renders tracking numbers as a table showing latest status (uses the UPS tracking Web service). Clicking on the tracking number link opens a page within the Drupal site showing the full package history, just as you would see on the UPS Web site.
I have included a couple of screenshots. This module, if contributed, would optionally integrate with the already Commerce UPS module (so that you would not have to enter your credentials twice.)
I have done a lot of custom Drupal development in the last couple of years but this would be my first contributed module. Thoughts?