Me too, I wrote my own tanzaku wishes a few years ago, when I participated at the Shitamachi Tanabata Matsuri...
It is believed that the custom started from the story of Orhime and Hikoboshi who, like the tradition says, are allowed to meet each other only on Tanabata. They are separated by a river and if it rains they will not be able to cross the river and meet. So, the people started praying for good weather, and this is how the tanzaku custom was born!
I've seen a lot of beautiful tanzaku trees, but probably because of the traditional setting, my favorite was this one from the Asakusa Shrine at Senso-ji, Tokyo:
EXIF info:
Nikon D300
Lens: 18-70mm F/3.5-4.5G
Focal Length: 18mm
Aperture: F/5.6
Shutter Speed: 1/400s
ISO Sensitivity: ISO 200