1UP believes Blizzard is working on a WoW expansion called World of Warcraft: Wrath of the Lich King:
We've trolled the German USK (game ratings) site for new release info before, but the fellows over at MMO Gamer were kind enough to point us towards their latest discovery. By typing "World of Warcraft" into the site's search bar, one will discover a mysterious listing for "World of Warcraft: Wrath of the Lich King (GC-Demo)".
The "GC-Demo" part of the title probably refers to the Leipzig Games Convention, which will happen at the end of August. With Blizzard's Blizzcon event happening this weekend and serving as the most likely place for the expansion to be officially announced, it's likely that a demo of will be shown at Leipzig.