Final Fantasy XIV these days. In the most recent live Producer's Letter, Naoki Yoshida made it clear that while it's not everyone, the game has certainly attracted sizable numbers. Over one million unique logins have taken place since the launch, with an average of 617,000 unique daily logins and a concurrency peak of 344,000 users, which is pretty good when you take into account the game's troubled launch history.
But the development team isn't focusing just on the past. The game's first patch is in the works; it's due to hit the live servers this year, and it contains a lot of extra content. Housing will be included, as will the game's first PvP arena and new extreme difficulty fights for each of the Primals. The patch will also include a new Primal fight against Good King Moogle Mog, hard modes for two dungeons, a new dungeon, daily quests, random matching rewards, a treasure hunting system... a lot of stuff, in other words. So maybe those million unique players are on to something.
[Thanks to Scott for the tip]