This package provides a tinymce plugin for easily adding youtube videos.
Only tested with latest Products.TinyMCE.
You'll likely need to allow iframe as a custom tag via html filtering for this plugin to work.
Due to the way most modern browsers help protect against XSS attacks, after you save a form where you added a video with tinymce, you'll likely see the rendering of the video is blocked initially. Just reload the browser once more to see the video added.
See http://glicksoftware.com/blog/disable-html-filtering for tips on getting around this annoyance.