jQuery is an excellent JavaScript library. On one side it’s easy to learn, on the other there’s already thousands of free plugins available. It’s slogan is “The write less do more library”.

This list is a live document with the best and most reusable jQuery plugins that I know.

Graphic User Interface

• jQuery UI – Provides abstractions for low-level interaction and animation, advanced effects and high-level, themeable widgets, built on top of the jQuery JavaScript Library, that you can use to build highly interactive web applications
• jQuery Mobile – Touch-optimized web framework for smartphones & tablets
• Datatables – It is a highly flexible tool, based upon the foundations of progressive enhancement, which will add advanced interaction controls to any HTML table
• Scroll Path – Scroll in any direction
• Tubular

Typography

• Fittext – Makes font-sizes flexible. Use this plugin on your fluid or responsive layout to achieve scalable headlines that fill the width of a parent element
• LetteringJs – Easier and flexible font use on the web

Graphics, animation and photography

• Spritely – Animations using sprites
• jQplot – Line, bar, piechart and other graphics
• Chart.js
• jQuery Visualize – Transform tables into charts
• Phantom.js – Powerpoint-style presentations on your browser
• Projekktor – Html5 video player with api for interacting with video
• Mapbox – Zoomable jQuery Map Plugin
• SwfObject – Insert flash files easily
• ImageMapster – Lets you activate HTML image maps without using Flash
• jQuery Transit – Super-smooth CSS3 transformations and transitions for jQuery
• Bigvideo – Videos as background images. Check also Tubular for Youtube videos
• Before/After Plugin – Show the differences before and after a photo
• Animate.css – CSS3 + jQuery animations
• Vegas – Slideshow with Image backgrounds

API’s

• Tweet – Put a Twitter stream on your website using the Twitter API
• Gfeed – Put an RSS feed on your website using the Google API
• jHere – Maps made easy
• Sharre – Allows you to create nice widgets sharing for Facebook,
  Twitter, Google Plus and more.
• Spectragram – Use Instagram API with jQuery. Check also jquery-instagram
• gmaps.js
• Social feed

Utilities

• Validation – Easy, flexible and unobtrusive validation of forms
• Sisyphus – Saves form data so user’s don’t loose it if they close the browser
• Cookie – Cookie management
• jStorage – Storing data on the browser using html5 localStorage
• Waypoints – Makes it easy to execute a function whenever you scroll to an element.
• jQuery life stream – Create a life stream from social networks
• jQuery Timelinr – Give more life to the boring timelines. Supports horizontal and vertical layouts, and you can specify parameters for most attributes: speed, transparency
• Aware.js – Make Your Site Reader Aware
• Typeahead.js – Autocomplete plugin

Other interesting scripts that aren’t jQuery plugins:

• Head.js – Load JavaScript script files efficiently
• Modernizr – Html5 features detection
• Moustache.js – Easy templating with JavaScript. See also Handlebars for some extra features.
• Popcorn.js – Video that interacts with the web page surrounding it
• Raphaël – Vectorial graphics and animations on the web
• Buzz – Html5 audio library