I personally use Mobil 1 0W-40. I have used Mobil 1 for 30+ years with excellent results, it is widely available and relatively inexpensive. The 0W-40 is a "light" 40 that holds up well to driving in the desert mountains without danger of "shear-down".
However, if changed at 5-6K miles (or 200 hours of engine operation, whichever is less), any good quality synthetic motor oil of the right grade will do a great job.
Lots of folks like the BMW 0W-30, Royal Purple, Amsoil, as well as many of the German group IV base stock oils.
If you change the oil while the add pack is still intact (additive package contains many sacrificial elements that actually get used up as the oil oxidizes and takes on contaminants such as water, coolant and fuel blow-by) any good synthetic will do the job.
Last edited by bimmerfan52; 12-06-2012 at 09:24 AM.