I discussed this in detail in this thread with a fellow member who had very high tire pressure/noise vibration:
http://f15.bimmerpost.com/forums/sho...=tire+pressure
Front: 35-36
Rear: 42-44
That's for 21" tires, but is close to stock values for almost all tire sizes if you look on the driver side door - it should have some numbers there. My front are 35 and rear are 42 for my 22" tires.
As long as you you stay within that range, you're good.