I was looking through the service and warranty info manual that accompanied the vehicle manual. Here's what I've gathered and I figure it could help anyone who's past the 4-year ownership mark and must keep an eye on things themselves:

CBS (condition-based service via onboard computer):
engine oil (Mobil 1 5W-30 or 5W-40)
oil filter
vent microfilter
air filter
brakes (assuming rotors at same time)
brake fluid
vehicle check
state inspection

Annual
engine oil/filter
state inspection
maintenance checks (ie. brakes, coolant level, power steering fluid level - mine was extremely low after 4 years, etc.)
spray underbody in the spring (plain water)

every 2 years
brake fluid

every 3rd oil change
intake air cleaner
air filter element

100k miles
spark plugs
ATF

120k miles
O2 sensor

"lifetime"
engine coolant

But what about things like belts? What else is missing?

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'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr