According to Japan's Nikkei Net (via IGN), Square Enix is working on a sequel to Final Fantasy XI. The upcoming MMORPG is being developed for PC (Vista), PlayStation 3, and Xbox 360. Prior to this revelation, Square Enix had hinted at a new MMO project, previewing a trailer featuring a 'next-gen' MMORPG engine. However, at this time, it's unclear if the FFXI sequel is indeed the game that will utilize this engine.
[Thanks, Master X]