Overview: a lecture with code examples showing folks how to get started creating a module including working with Drupal APIs
I gave this talk several weeks ago at Saturday House where it was well received. It covers an introduction to the hook system, then shows basics of the most common hooks like hook_menu, hook_nodeapi, and hook_form_alter. In addition to slides, code snippets are added to a new module, then run to show off how each snippet works. The talk includes dealing with gotchas like menus and caching, and how to interact with the database.
You can see more details at http://groups.drupal.org/node/10202 including the slides and the completed module.