Colorbox - a jQuery lightbox
A lightweight customizable lightbox plugin for jQuery
Colorbox is a jQuery plugin, meaning that it extends the jQuery JavaScript library to include extra functionality.

Released under the MIT License. Source on Github (changelog).

Compatible with: jQuery 1.3.2+ in Firefox, Safari, Chrome, Opera, Internet Explorer 7+

Supports photos, grouping, slideshow, ajax, inline, and iframed content.
Lightweight: 10KB of JavaScript (less than 5KBs gzipped).
Appearance is controlled through CSS so it can be restyled.
Can be extended with callbacks & event-hooks without altering the source files.
Completely unobtrusive, options are set in the JS and require no changes to existing HTML.
Preloads upcoming images in a photo group.
Currently used on more than 1.9 million websites.

Instructions & Help
The FAQ has instructions on asking for help, solutions to common problems, and how-to examples. First-time jQuery users can check out the Colorbox Beginner's Guide. Intermediate users can probably glean everything needed by view-source'ing the demo pages.

Usage
Colorbox accepts settings from an object of key/value pairs, and can be assigned to any HTML element.