jQuery UI is a budle of UI widgets, components including drag and drop, sortable, resizable, slide, table sorter, tab, dialog, magnifier, etc.

All UI widgets support theming and you can download the component(s) only you want.

jQuery Form plugin is good for unobstrusive ajax form implementation.

This plugin supports 'ajaxForm', 'ajaxSubmit', 'From validation', 'JSON', 'XML' etc. And more, you can ajaxify file upload using this plugin without any other extra work. One of my favorite!

I thinks this plugin must be included in the jQuery core. :)

Form validation can be very time consuming work. This plugin lets you add various form validation functionality with ease. It is very easy to use, and supports built-in validators like email, url, etc.

If you are plan to implement form validation, take this plugin. Highly recommendable!

Demo Documentation(Well done)

Live Query utilizes the power of jQuery selectors by binding events or firing callbacks for matched elements auto-magically, even after the page has been loaded and the DOM updated.

Jeditable plugin is a inplace-edit plugin which supports normal input/textarea, inlined select, custom event trigger, etc. Using this plugin's extention point, you can build your own inplace-edit plugin.

BlockUI plugin can block UI as it's name, but doesn't block browser. :)

This plugin is good for simulating synchronous ajax call using asynchronous ajax call.

One of famouse jQuery thickbox plugin.

Lightweight and simple modal plugin. Looks good.
See a demo.

FCKEditor is a very popular rich text editor. But FCKEditor is easy to integrate and use, then what is the strength of this plugin?

• First, you can intergrate FCKEditor MORE easily.
• Second, this plugin support jQuery Forms plugin, so you can ajaxify form submission of FCKEditor without any extra works. Good!

jCarousel Lite plugin is a lightweight carousel widget.

This plugin is just about 2KB, but very flexible.

jTagging is good for implementing fancy tagging UI.

If you want to provide sexy tagging look, check this plugin. :)

Are you want to provide good-looking tooltip to users?

Check jQuery Tooltip plugin. This plugin supports not only text tooltip, but also image tooltips. Recommend you.

Impromptu plugin provides pleasant way to spontaneously prompt a user for input. Great replacement for alert box. :)

Treeview plugin renders html list in tree form.

Good for navigation implementation. How about allowing editing users to organize tree with nestedsortables plugin and render it with treeview plugin? :)

Cycle plugin is a lightweight slideshow plugin. It supports many fancy visual effects including shuffle, zoom, fade, turndown, etc. Cool~*

jdMenu plugin provides a clean, simple and elegant solution for creating hierarchical drop down menus for websites to web applications.

jQuery based universal markup editor. markItUp! is not meant to be a “Full-Features-Out-of-the-Box”-editor. Instead it is a very lightweight, customizable and flexible engine made to meet the developer's needs in their CMSes, blogs, forums or websites. markItUp! is not a WYSIWYG editor, and it never will be.

Interface Element plugin provide similar components with the jQuery UI like the draggable, droppable, sortable, etc. jQuery UI is the official plugin so I use jQuery UI instead of the Interface Element plugin usually. But I think sortable plugin of Interface Element is more stable and better than jQuery UI's sotable plugin. And Nestedsortables plugin is based on Interface Element's sortable plugin.

Nestedsortables plugin allows you to sort and nest elements using drag and drop.

This plugin lets you make corner without images. It uses canvas(FF)/VML(IE) for making corner. Recommendable!

Corner plugin makes corner without using images. It support various corner effects. This plugin addes a lot of divs for making corners.

Show big code block in small area, and users can expand small area to see full code.

Similar to a horizontal accordion navigation, or holding some playing cards in your hand... sliding panels around to reveal one of interest. This is a plug-in for the jQuery JavaScript Library and it requires the hoverIntent plug-in. By design the panels are positioned using percentages so they will naturally scale with your page layout and user-selected font size. - from plugin site's explanation

This plugin supports good-looking tooltip. You can also use ajax for tooltip contents. Recommendable.

jQZoom plugin allows you to realize a small magnifier window close to the image or images on your web page easily.

jqGalScroll(jQuery Gallery Scroller) plugin makes smooth scrolling photo gallery using image list.

Select box manipulation plugin provide convenient ways to manipulate html select box.

Color picker plugin.

Ajax based grid plugin.

Kwicks for jQuery is a plugin that simulates the insatiably attractive Mootools effect of the same name.

jQuery plugin for the star rating system.

jQuery plugin that makes it easy to build up a tree of DOM nodes.

Manipulate cookies easily with this plugin.

jQuery plugin for turning a standard HTML table with THEAD and TBODY tags into a sortable table without page refreshes. tablesorter can successfully parse and sort many types of data including linked data in a cell.

Play your MP3 file on the web easily with this plugin.