The demo includes both a YouTube and Vimeo iframe embed, both at different aspect ratios. Both fluid, both 100% width.
FluidVids.js tested in Chrome, FireFox, Opera, Safari, IE7, IE8 and IE9.
ClassyBox is a jQuery plugin that is a complex LightBox alternative with support for the most popular video services, enabling you to embed a media gallery on your site.
YoxView is a free Lightbox-type media and image viewer jQuery plugin. It's easy to use and feature-rich. Images, videos, inline content, iframes, Flash contents are supported.
By combining support for a wide range of media with gorgeous skins and a user-friendly API, Lightview aims to push the Lightbox concept as far as possible.
rlightbox is a jQuery UI mediabox that can display many types of content such as images, YouTube and Vimeo videos. It has many unique features like Panorama and Live Re-size. Like other jQuery UI widgets, it is ThemeRoller ready.