My first car was Vicki, short for Victoria, in a queens-of-England theme to match with my dad's (Betsy, short for Elizabeth) and mom's (Anne).
The first car I shared with DH was "Bitty" - short for "the bitty blue bullet" because it was tiny (and, obviously, blue).
Later he had a black 4-door called Jeeves, and I had "Miss Emily the War Wagon" (Emily or Emmy for short).
My current car is officially "Samantha" - because it didn't seem right for her to go unnamed. But it doesn't have a reason like the other names, so I never really use it.