What are the "must have" jQuery plugins?

My list:

• Autocomplete
  • Input field to enable users quickly finding and selecting some value, leveraging searching and filtering.
• JSON
  • JSON plugin retrieving retrieving and manipulating json data.
• Cookie
  • Simple & lightweight utility plugin for reading, writing and deleting cookies.
• Vaildation
  • For validating form input data.
• UI
  • Full-featured themable and ready-to-use widgets and more...
• Interface
  • Dragging, Sortables, Droppables, plug-and-play components and visual effects.
• Cycle
  • Versatile and lightweight image slideshow plugin.

We currently use:

Most impressive

• Layout (dock, pin, splitter) - just amazing

Jquery UI elements:

• Tabs - tabbed UI
• AutoComplete - suggestion box from web service
• DatePicker - nice calendar date picker

Useful community plugins:

• Scrollable - scrolls any div
• Scrollpane - control scrollbar appearance
• Table sorter - table sorting (client-side) for any simple table
• QuickSearch - instant searching of table content
• Validate - form validation (required / type / custom regEx)
• HotKeys - traps for key shortcuts. Captures EVERY key on the keyboard. Awesome.
• BlockUI - awesome modal dialogs
• Curvy Corners - anti-aliased by default
• Tokenised input (or Facebook autocomplete with Xs) - Facebook style tokenised autocomplete

More to come, I'll add links etc...

I think that Flot plugin (a plotting library / plugin) deserves a place in this "must-have" list.

In addition, it is used here, in StackOverflow, to display the histogram of the reputation in the user account page.

I'll list one I'm working on...

My jLINQ plugin is a jQuery version of .NET LINQ. It's made for working with in-memory collections (not talking directly to the server) and let's you use syntax similar to the following.

var results = $.from(data)
    .ignoreCase()
    .startsWith("firstName","m")
    .or("n")
    .isNot("administrator")
    .orderBy("lastName")
    .select();

It supports a bunch of other commands that you find in LINQ for ordering and grouping along with most of the selection commands like contains, between, greaterThan, etc...

Here is a demo - It's stable, but still in progress

Maybe not must have, but might be useful as it progresses...

I just found jqGrid and it looks very good.

and it also has lots of documentation (right now a 99 pages pdf) and examples

• jQuery UI
  • For Tabs, sortable lists, custom animations, drag and drop, etc.
• AJAX Form (http://malsup.com/jquery/form/)
  • Changes your forms so they submit an AJAX request.
• Cycle (http://malsup.com/jquery/cycle/)
  • For creating carousels, or an area which cycles through an array of data (images, text, etc)
• Validation (http://bassistance.de/jquery-plugins/jquery-plugin-validation/)
  • For validating form input.

For an unobtrusive way to send messages to the client without affecting the page's content permanently, I use jGrowl, based on the OSX Growl system.

Lot's of options, settings, and it keeps the page clean : )

jQuery tools from Flowplayer is really fancy. I really like the expose and overlay plugin.

UI - no better way to do draggables, resizables and few others.

Slibox2 - ultimate lightbox clone for jQuery, very easy to use.

iFixPng - simple solution for IE6 PNG w/alpha.

I have been very impressed with the Filament Group's Date Range Picker

UI is definitely a must-have. As a grid component, I would recommend jqGrid. IMHO, it is better than flexiGrid.

If you're using Visual Studio 2008 to code your jQuery you need the Intellisense: http://weblogs.asp.net/bleroy/archive/2008/10/27/jquery-intellisense-documentation-file-available.aspx

http://docs.jquery.com/Plugins/dimensions , it has great offset and outerwith functions...

I'm a big fan of jTemplates, which gives you client side templating. I find it extremely powerful, especially for rendering results.