Resources for learning WordPress Hooks

1. If you just read one book about WP development, read Professional WordPress Plugin Development. Thanks to Chapter 3, I totally got the idea of what Actions and Filters are.
2. Actions list: find out which actions run during a typical request on front end or admin page. This is a good resource to figure out when to use which action hook.
3. Filters list
4. An article from Smashing Magazine on WordPress Hooks

If you're interested in writing your first WordPress plugin, you could read my article here.