I think everyone has mentioned the new car purchase rebates but joining BMWCCA has other perks. There's DIY Forums and Chapter meet ups so you can learn more about your car. Also there's discounts available for parts and non-warrantied service at certain dealerships and independent BMW shops and tuners!
The more active your local chapter, the more perks and benefits available!
2012 550xi MSport - everything but TV's in the head rests!