Today I heard the rumor that Porsche plans a Cayenne facelift for the MY 2006.
This facelift is rumored to include substantial changes to the front design (front lights, engine hood, front air inlets) and rear design (larger rear window, different rear lights).
Other rumors also indicate a moderate power increase for the Cayenne S and Turbo and...hold your breath...a Cayenne V8 Diesel with aprox. 300 HP (apparently european customers strongly demand a Diesel).
There is also a rumor that Porsche plans to offer an Entertainment System for the Cayenne including a DVD player and one central flip-down TFT screen in the middle of the roof or two TFT screens in the front head rests.
More rumored future options: Satellite Radio (US only), MP3 Player as an add-on to the current PCM2, Targa roof, Turbo Powerkit and a more sporty setup for the Air Suspension.

As always: rumors have to be taken with a grain of salt.