Some of the sites that Metro Browser has full, built in support for are MegaVideo, VideoZer, VideoBB, and YouTube. Metro Browser claims its efficient design allows for video streaming even over 3G as well as the ability to handle large video files in the device’s memory rather than requiring free storage on the device.
The app currently has mixed reviews. A free trial is available to see if Metro Browser suits your needs. If it's perfect for your web browsing and video streaming needs, the full version can be had for $1.99.
source: Windows Phone Marketplace via WPCentral