I came across a very interesting read the other day in 'The Science of Flowers and Feelings' - an article about the effect that receiving flowers can have on our moods.
It details a study showing that people's moods instantly improved upon receiving gifts of flowers, and that their moods were still higher when tested again after a few days. Having received sunflowers last week as a Thank You gift, I can absolutely relate to this. The flowers are still looking gorgeous, and bring a smile to my face each time I walk into the room and see them.
So if you're looking to cheer someone up, and keep that feeling around a while, flowers are definitely a good way to go!