Ageia PhysX Processor
 

Who's gonna be getting one?
Seems a £400+ CPU and £500+ of graphics power just isn't enough nowadays.
Info here.

Some demos here and here

All the overclockers games machines have them as standard now :) They will be built on to the next gen cards anyway IMO

When UT2007 comes out, I'll get one :)

PS. AFAIK, Nvidia plan to off load some physics processing to the GPUs using their drivers + new architecture, but thought it was all in house stuff, not PhysX?

Yes Nvidia are developing the Havok FX engine which was used on HalfLife2.
Unsurprisingly, ATi have something else as well.