The End

The End is an other-worldy dimension soon to be introduced into the Minecraft Universe, mentioned by Notch. It may not be the official name for the Sky Dimension, 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. Since it is a planned dimension, not much is known about it yet. You cannot enter the Ender in 1.9pre3

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 9th of October 2011, at around 9:20am (+1), 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 Jeb said "I KNOW there is a portal in here because of the debug logs".

Trivia

 * The random Ender-Portals in Strongholds may explain why there are Endermen outside of their native dimension.
 * In order to enter the Ender, you need to have access to both the Overworld AND the Nether.
 * Unless you have an inventory mod, you can't seem to access the End without involving some combat beforehand (you'd have to kill at least a few Blaze and Endermen to get their respective items).
 * The End requires you to kill many endermen, then, use obsidian to make a portal to the Nether where you must kill Blaze (s) to get the rods. Then turn the rods into Blaze Powder and add Ender Pearl (s) to make eye of ender (s). You must then find a stronghold and apply the eye of enders into the air portal frame.