While developing the DevoutGeek.com site, I created a number of Magento extensions. The first extension that I created was Configurable Colors. This extension creates color swatches in place of the color drop-down for configurable products. I created a jQuery plugin to display the color swatches and make ajax calls to the extensions controller method to display the relevant images. Through a bit of trial and error, I learned a great deal about creating Magento extensions (and incorporating jQuery into them).
There are many articles that discuss how to create Magento extensions, so this post discusses how to incorporate a jQuery plugin into the extension. For information on how to create an extension, read this.