HTML5 is a new and updated version of HTML and XHTML. The HTML5 draft specification defines a single language that can be written in HTML and XML. The new standard incorporates features like video playback and drag-and-drop that have been previously dependent on third-party browser plug-ins such as Adobe Flash and Microsoft Silverlight.
Check out the following list showing some excellent examples of sites that are already using HTML5.
If you know anything missing that can be a great addition to this list, you can suggest by using the comments box.