The jquery.com Plugin Repository at http://jquery.com/Plugins/ is a great place to start when looking for documentation. Each plug-in listed in the repository has a link to a page from which the plug-in can be downloaded. Additionally, many of the linked pages contain demos, example code, and tutorials to help us get started.
Official jQuery plug-ins also provide ample comments in the source code itself. For many plug-ins, the comment syntax matches the comments of the jquery.js file, providing a description and at least one example of each method. This means that the tools available for viewing jQuery documentation also work with compliant plug-ins.
For example, the .offset method of the Dimensions plug-in has these comments:
/**
* Returns the location of the element in pixels from the top left
* corner of the viewport.
*
* For accurate readings make sure to use pixel values for margins,
* borders and padding.
*
* @example $("#testdiv").offset(...