Version b14 has been released. You can download it here - http://cesium.agi.com/downloads.html
This release is the first to include support for worldwide terrain rendering, as well as our new animation widget. Checkout the blog post on this release for more information: http://cesium.agi.com/2013/03/01/Cesium-version-b14-released/
For a list of all of the changes, see the change log.