dropdown.dot.js is a jQuery plugin for super-flexible dropdowns based on dot.js templates.  

YoxView is a free Lightbox-type media and image viewer jQuery plugin. It's easy to use and feature-rich.  

DateTimePicker is a jQuery date and time picker plugin. You can use this plugin to unobtrusively add a datetimepicker, datepicker

GalleryView is a jQuery plugin for creating a wide variety of gallery types, including carousels, sliders and slideshows.

PNotify is a JavaScript notification plugin, developed by SciActive. Formerly known

Stacks is a jQuery plugin to create iOS list-style stacking headers. It recreates the effect from iOS contact lists etc.

jsTree is jQuery plugin, that provides interactive trees. It is easily extendable, themable and configurable, it supports HTML & JSON data sources

leanModal.js is a super simple JQuery plugin for modal windows that works with your CSS. It is built for all the short dialogs, alerts

Selectize is the hybrid of a textbox and <select> box. It's jQuery-based and it's useful for tagging, contact lists, country

Avgrund is a jQuery plugin for modal boxes and popups. It uses interesting concept showing depth between popup and page.