TopUp is an easy to use Javascript library for unobtrusively displaying images and webpages in a Web 2.0 approach of popups. The library is jQuery and jQuery UI driven in order to maintain cross-browser compatibility and compactness. TopUp offers the following advantages:

• TopUp is absolutely free, also for commercial use (view the license)
• A very easy setup process: only one(!) include and nothing more
• Using TopUp presets keeps your HTML code 100% clean, no extra code needed whatsoever
• The ability of displaying images, flash (from sites like Youtube, SWF and FLV files), movies (QuickTime, Windows Media and Realplayer), iframes, DOM elements and raw HTML
• TopUp can be used along with Prototype (just include TopUp before Prototype)
• TopUp is compressed with Yahoo! YUI Compressor to 47.6 KB (includes JS, HTML and CSS)
• Usage of CSS sprites to reduce the amount of image requests to two per layout for faster loading
• Cross-browser compatibility
• Fancy layouts, animations and transitions
• Auto-correction of size and position when required
• The possibility to create groups
• Support for AJAX requests
• It’s open source: check out http://github.com/archan937/topup and enhance TopUp yourself!
• And many more…

via The #1 Javascript Pop Up / Lightbox – Get TopUp – Home.