There's a sticky thread about hidden features which is very good, but let's have a think....
* The air con in the upper glove box,
* the three positions of the driver's centre armrest,
* the easy adjustment of the handbrake, under the cover between the rear seats (back of the centre console) although that's kinda commonplace now I suppose.
* it'll auto-lock the doors above 3Mph .
* you can open and close the windows (and roof, if you have it) by holding the plip key buttons
* holding down the play/stop button on the cd player will pause cd's - otherwise it just stops it.
* if you have a Connect or Connect+ stereo, you can fit a SIM card straight from the network's packaging (they usually come on those big plastic cards and you typically push them out? Don't, they fit straight in the car).
* the "follow-me" headlights that will stay on for x seconds after you've locked the car and walked away.
I dunno, some of those might be a bit obvious.