Microsoft has released an official MSN Video app to the Marketplace, which allows you to browse and search clips from the Bing Videos website. (Think of it as the MS equivalent of the YouTube app). Fitting nicely into the Metro UI, MSN video offers the option to watch in both regular or high quality. The HQ vids are obviously much nicer to look at, but as you may imagine, take significantly more time to load up and stream. One snazzy feature is that videos played from MSN Video will later appear in your history in the Music + Videos Hub.
With YouTube dominating the online video market, we're not sure how much MSN Video will catch on. That being said, it is great to see MS supporting WP7 by creating their own apps to make it fresh and increasingly useful.
You can download it here for free.