The exam for the class you never went to dream is fairly common. I still get that one once in a while.
I also get the radio/dead air dream occasionally.
The one that I get most often involves driving my car, needing to brake to avoid a collision, and finding that I'm sitting in the back of the car (from which the brakes are obviously, not easily accessible). Not comforting. I assume it has something to do with control issues.
There's another one that I have trouble remembering later but, when I'm in it, I think "it's that same dream again!"