Dropzone.js is an open source library that provides drag’n’drop file uploads with image previews.
Ajax Autocomplete for jQuery allows you to easily create autocomplete/autosuggest boxes for text input fields.
A fully responsive and lightweight jQuery dateinput picker
Via @Zraly
A powerful slider for selecting value ranges, supporting dates and more.
Touch support included.
4 kb of uncompressed JavaScript allows you to use <input type="color"> even for IE6+.
Some good thinking done by Chris Norström. Solves the confusion of the classical “iPhone slider”, where you are not sure if the visible status (OFF) is the active one, or you have to switch to get to it.
Nice UI for a “volume” dial built on jQuery.