Hi,

I´m new to the forums and just bought myself an x5.
However I have more experience on fuel parking heaters (since I live in Finland), such as:

webasto

http://www.webasto.com/products/en/3115_3422.html

or Eberspächer

Eberspächer UK - Water Heaters



Also, you can go for the cheaper (approx. 700USD) choice and install a plug heater (for the engine) with indoor heater (for the cabin), such as:
Calix
Calix AB

or

Defa
DEFA Warmup=#

Advantages with the fuel heater is the remote, you do not need to plug your car to electric outlet post, and sheer warming power (up to 10kw!)

I constructed a cellphone remote for my heater (which doubles as spare key), so I dial a number, and the car literally melts the snow off itself in half an hour.