Magento Widgets : Widgets are the most exciting features in the magento 1.4 .Magento widgets gave magento a new dimension from the user point of view . Magento widgets are very easy to use just enable the widgets in the CMS page of magento .
How to Develop a Widget :
Typically, developing a widget doesn’t differ much from developing a regular Magento extension which provides frontend functionality. If you want to allow a store owner to define different configuration options per block instance and to have full control over the placement of the block instance on a page (that also includes ability to add block into a CMS page or CMS static block) – the widget format will help you to do so.
Extension can then have any number of Magento Widgets. Widgets are typically related to the functionality which is provided by the extension itself. You can also develop widgets which add configuration options and placement control to the functionality which already exists in extensions.
Your Magento extension can also create and add pre-configured widget instances to defined pages right upon the extension installation.
Webkul’s Magento Extension’s : http://www.magentocommerce.com/magento-connect/developer/webkul