you can play 20 questions, too. someone thinks of an object, and the others have to ask yes/no questions to be able to try to guess what it is. is it hard? yes/no. is it red? yes/no. that kind of thing. it's fun.
riddles are a good car thing too.
you can also play the name game. you have to find each letter that's in your name in order. signs, trucks, gas stations...all good places to find letters.
Madlibs > all other car ride games