Chosen is a JavaScript plugin that makes long, unwieldy select boxes much more user-friendly. It is currently available in both jQuery and Prototype flavors.

jQuery File Upload – jQuery UI version

File Upload widget with multiple file selection, drag&drop support, progress bars and preview images for jQuery. Supports cross-domain, chunked and resumable file uploads and client-side image resizing. Works with any server-side platform (PHP, Python, Ruby on Rails, Java, Node.js, Go etc.) that supports standard HTML form file uploads.

jQuery UI Highlight Effect

Highlights the background of an element in a defined color for a custom duration.

jQuery UI Selectable

Allows groups of elements to be selected with the mouse.

jQuery UI Accordion

Displays collapsible content panels for presenting information in a limited amount of space.

jQuery UI Spinner

Displays buttons to easily input numbers via the keyboard or mouse.

jQuery UI Pulsate Effect

Pulsates an element n times by changing the opacity to zero and back.

jQuery UI Slider

Displays a flexible slider with ranges and accessibility via keyboard.

jQuery UI Autocomplete

Lists suggested words as the user is typing.

jQuery UI Widget

Provides a factory for creating stateful widgets with a common API.