My wife and I have always named our cars. Usually its based on the 'character' of the car.
The X5 is called Bertha. That should tell you we think she is big and/but beautiful and capable.
The previous, 325 convertible, was Clifford. Conservative and square but functional and loveable. The alarm system was really the source of the name

.
Then there was Harry. Yep, a Japanese boring Honda CRV. Destined for the scrap yard the day it was made. Sorry all Harry's out there.
Oh and Maria. I love her, she has strength and hairy armpits, and she is Italian. The car was a very old and unbreakable Alfa Alfetta that travelled 7,000 km (4,000 miles) across Australia on 3 cylinders with no complaints.