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If you are looking for a great jQuery plugin that you can work into your website, than the jQuery Rain website is a great place to start and has a large list that is continuously growing. Most of the jQuery examples are free and they provide working examples or code that you can download. Some have paid versions available as well, but very reasonable pricing.
The site is laid out in a very intuitive way. The navigation bar is created around what you would like to achieve, such as forms, animation, menus, etc.
You will always want to read the terms and conditions for any script you will would downloading in case it requires proper credit to the developer or other necessary steps needed to place it on your site.
You can browse the site here, www.jqueryrain.com