Bethesda, the makers of the Oblivion game, say that they are going to make an Expansion pack for the PC version called Shivering Isles.
The expansion pack claims that it will add another 32 hours of gameplay. This includes new areas to adventure, brand new quests, enemies, and more. The quests you take and the decisions you make will have a bigger impact on your character and the world around him/her/it more that it has before.
The Expansion continues on from the origional when a suspecious gate has appeared in Nibben Bay. Going through the gate you will lead to a new land called Shivering Isles which is in need of your help. The Shivering Isles is ruled by Sheogorath, who is the ruler of both isles, Mania and Dementia. Not much more is known on the subject.
The Expansion pack is supposed to release sometime during Q2 2007.