Sunflowers are very pretty and really easy to grow but when it comes to the really tall flowers, I like the Hollyhocks.
Hollyhocks are a flower that can be used to hide many flaws, to set off a fence as shown in the above picture and they also look very lovely when planted at the end of your outdoor shed etc.
Both the Sunflower and the Hollyhock are easy to plant and maintain, but as I said, I prefer the Hollyhock hands down.