Dibella's Watch adds an entire new continent to Oblivion. It comes complete with a major city, castles, towns, villages, farms, monasteries and all the good stuff that makes up a Medieval landscape. There's also fighting to be had and quests to be made!
The land is growing by the minute! This is the map of Beta 03, with many of the most interesting locations marked. You can indeed visit the Deadlands out west, but there's not much happening there as yet.