To dream that you are flying signifies a sense of freedom where you had initially felt restricted and limited.
To dream that you are flying with black wings signifies bitter disappointments.
Dreaming that you are flying underwater represents control over your emotions. You are comfortable with confronting your feelings directly.
To have a dream of a flying car means that you are doing exactly what you want to do in life. You are in charge of where you are headed and your goals.
*For an in depth analysis, see Common Dreams: Flying.