The Examples modules

If you are new to developing for Drupal 7 or upgrading from another version, the examples modules is a GREAT module for examples on how to develop for Drupal using the API. It gives you the basic of a lot of the common things you do when developing. Some examples included are theming (hook_theme), running cron job (hook_cron), forms (hook_form, hook_element_info), menu, node and so much more!!