As the 2nd owner of my X5, I purchased it a month after it came off out of warranty. Good news is that it only has 34000 miles on it (2008 model). But the BMW SA in Mt. Laurel, NJ told me that there is not a BMW warranty available to me, as a 2nd owner. There is a maintenance plan that will allow me to take it in for inspections, oil, wiper blades, belts and brake pads/discs/fluids. I think the cost was about $2400. Seems high. I can do my own brakes, and the other things will not cost me $2400 over the next 4 years.
For an actual warranty plan to cover repairs/malfunctions, he said I'd need to shop 3rd party providers since it's not something this dealership gets involved with.
From what I read here, it looks like there are some dealers who will assist with this. As of now, I've not chosen anything...