Fitvids.js is a lightweight, easy-to-use jQuery plugin for fluid width video embeds. It makes sure that your videos scale to fit the space, and don't break your layout.
This Drupal module lets you easily add FitVids.js to your site, and to quickly configure it using Drupal's admin pages.
The latest versions are
It supports YouTube, Vimeo, Blip.tv and Kickstarter by default, and can use it with other video providers like Facebook or Viddler.