TextMate Drupal Bundle the php script builds the function list against your drupal source (details on the page).
Drupal.tmBundle makes it easy to create FormAPI arrays..."contains tab triggers for almost all forms api stuff."
Drupal Helper Textmate Bundle is a simple bundle with often used hook implementations, form api and menu stubs, and variable handling snippets. There is also a screencast with the basics of how to use it.
The Drupal handbook TextMate + CVS or Diff bundle page provides details on installing and using the bundle.
You can use a TextMate command to look up Drupal API functions and Drupal core hooks at api.drupal.org. You can then simply place the caret on the function name, press a shortcut, and get the documentation.
See also: https://www.drupal.org/project/textmate