Level 5 - developer of the Dark Cloud series and the next installment in the Dragon Quest series - recently updated its website with a teaser image for a new PS2 RPG, seen below:
There's no word on what the game could be, though people may recall the story ran in April about Level 5 working on a third title in the Dark Cloud series. The game is to feature a more sci-fi feel, and will have a darker feel than the previous games. While this much is guesswork, the feel of the picture and things such as flying cars make it seem plausible.
Whatever the teaser is actually for, RPGFan will keep you updated as more is revealed.