Magento: Events and Observers

One of the greatest feature in Magento is Events and Observers.

You can add any functionality for the specific Event without following:
1. Modifying core files
2. Copy core file to local folder
3. Override Core files
4. Extend core methods

Here are the links for best examples:

1. http://codemagento.com/2011/04/observers-and-dispatching-events/
2. http://magedev.com/2009/08/11/magento-events-create-update/
3. http://magedev.com/2010/10/15/adding-event-observer-on-the-fly/

You can create custom events in your Own module as well

Using events is the best way of extending Magento functionality......