modules

• Better breadcrumbs — http://drupal.org/project/hansel
• Views infinite scroll (there are two, one is better it looks)

The Difficulty of Identifying All Hook Implementations

explained by Matej Midriak (wapnik):

Sorry i don't have time now to examine the code to find all those
patterns (if that's even possible without reading the entire drupal
sources), but here is one example.
In drupal_mail() function:

Agaric Design Collective's standard project starter distribution, stored as a git repository from which cloned projects can pull updates (upgraded modules or core and new additions), consists of Drupal 6 core and the following excellent contributed modules drawn from the thousands publicly available on Drupal.org.