Rumour being circulated by GamesIndustry.biz has it that Sony is working on a Wiimote-esque controller for the PS3, motion sensing and all, which will also be able to split into two parts - nunchuck style perhaps? Supposedly each segment would contain an accelerometer, presumably offering similar sensing to the current Six-Axis controller.
Apparently already with a few development partners, whether those are (games) developers, potential manufacturers or what is unclear, it's unclear when Sony will officially make an announcement. It's even possible this is just a prototype, proof-of-concept unit that will never see the light of day.
The intention is apparently to allow the PS3 to try and emulate, or even better, some of the games that have been so successful for the Wii. This implies, to me at least, that we can expect a radically different design to the current DualShock3 and Six-Axis controllers, probably better suited to being embedded within various peripherals - a la the Wii Wheel and Wii Zapper.
Realistically we'll have to sit and wait for Sony to speak its piece on this before we can speculate further. Meanwhile check out our artist's impression above for an idea of what it definitely won't look like.