It's not just rumors now as Square Enix has announced Final Fantasy XIII-2 as being due for the PS3 and Xbox 360 in 2011.
FINAL FANTASY XIII-2 OFFICIAL TEASER
The director has been announced as Motomu Toriyama – the man behind that game’s notorious “story-centric” linearity. But he does promises that the next game will return its town and shop "elements". (Typical and standard in J-RPG)
Also announced were a handheld port RPG to the PS3 exclusives - Final Fantasy Versus XIII.
*edit*-youtube video deleted by SquareEnix.