The End

The Ender is a dimension soon to be shown, mentioned by Notch. It is possible that this is the official name for the Sky Dimension, but unlikely due to the vast difference in landscape and features. This dimension will be home to the Endermen and Enderdragons. The dimension seems to have a green ambient light.

History
Notch tweeted "raqreqentba", which could be decoded using ROT13, translating to "enderdragon." A Reddit user under the name of "cptqwashi" posted the idea that the new dimension accessed by the new "Crystal Block Portal" would be called the Ender, and would be home to the Endermen and Enderdragons. Notch soon gave more information and said that cptqwashi was "100% correct."

Finding an Ender Portal
On 10/9/2011, at around 9:20am (+10), during his gameplay stream, Jens began searching for an Ender portal. This appeared to be done by throwing an Eye of Ender, which appeared to float briefly into the direction of the nearest ender portal. It is unsure as to whether an eye leads to a portal, or to a stronghold (portals are situated in strongholds) because it was implied that there was a possibility that there could not be a portal inside a stronghold. This was evident when Jens said "I KNOW there is a portal in here because of the debug logs". Pictures are below

Trivia

 * The random Ender-Portals in Strongholds may explain why there are Endermen outside of their native dimension.