According to the website Fast Games News Online, Sony has yet begun working on the next generation of consoles, and chosen to drop nVidia, producer of the actual RSX, in favor of PowerVR as the provider for the GPU.
PowerVR has a long story in the gpu development, with successfull products like the Kiro series, the gpu on the Dreamcast, and the majority of actual high-end Smartphone and gadget like the Apple iPhone and the Palm Pre.
PowerVR products are very popular at the low-power market, due to a combination of excellent performance and low power requirements, due to their proprietary technology based on tiles (Tile Based Deferred Rendering).

The same website states that also the PSP2 will be built around another PowerVR gpu, the SGX543MP4 (four cores) 133M poly/s, with fill rates in excess of 4Gpixels/sec @200MHz.

Origial article:

We can officially reveal in this world exclusive that SCEI has officially chosen the Imagination Technologies currently in development PowerVR Series 6 architecture for it's next generation PlayStation console scheduled for 2012 worldwide deployment.

The PlayStation 4 shall use a high end variant of the Series 6 line. Performance, specifications and features are at this time unknown. The Series 6 shall receive an official announcement from IMGTEC sometime in 2010, with initial models targeting the smartphone and netbook sector.

It is believed that Sony has gained exclusive rights to the technology for the console space.  

IMGTEC's PowerVR technology uses an advance technique called TBDR which can outperform a competing IMR product from nVidia/ATi by 3-5 fold whilst maintaining equal die size and price point. TBDR was the primary reason the SEGA DreamCast was capable of such astonishing graphical feats as early as 1998.

Interestingly SCEI has also chosen IMGTEC as the graphics provider for their next generation PSP. That particular product shall however be using the Series 5XT.

http://fgnonline.webs.com/