Likely the most SEO-optimized plugin I’ve written yet (156 downloads in 12 hours with no promotion), Video Embed Widget makes it easy to embed videos in your WordPress sidebar only knowing just the URL. Specify the maximum height and width, hit save, and you’re live. Not only that, the widget generates embed codes using the Embed.ly API which supports 151 service providers and counting. You can embed Flickr photos, XKCD comics, and videos from the White House, all in the same sidebar.
Download Video Embed Widget at WordPress.org, leave questions or ideas in the forum, or fork it on GitHub.