See also: Difference between "banner" and "flag".
I would like to know about standard, too.
What would you say are the differences between the three words?
Banner is typically long and horizontal - you'd see it hung over a street, for instance, across the width of the street.
Flag is like a national flag, also rectangular, but closer to a square in proportion.
Standard is a triangular shape usually hung from bunting on a ship.