YouTube has added an extra-large (850×500) video player for clips that are available in HD format (see example). Also, there’s a new HD option in YouTube browser that lets you quickly filter all HD videos on a page. Thanks Andy.
While there’s no option to search for only HD videos in YouTube, you can easily extend the high-res trick to easily locate HD clips on YouTube through Google. Your search query should be something like this:
matt dance site:youtube.com “watch in normal quality watch in HD”