Tanabata (七夕) meaning "evening of the seventh" is a Japanese festival that originates from the Chinese Qixi Festival. It is in celebration of the meeting of the deities (and lovers) Orihime and Hikoboshi, and according to legend, they are only allowed to meet once a year on the seventh day of the seventh lunar month of the lunisolar calendar. In Japan, it is celebrated by writing your wish on a piece of paper and attaching it to a bamboo tree.
Tamagawa Sengen Shrine - known as the Godzilla Shrine has an annual Tanabata festival, with potted bamboo trees decorated with Tanabata streamers. Visitors can write their wish on a piece of paper and attach it to one of the bamboo trees.
A simple Tanabata festival with bamboo trees, and Tanabata decorations. There are even some shrine cats that occasionally make an appearance.
Shitaya Shrine hosts events all throughout the year, which includes their Tanabata Festival. They are popular for their goshuin (shrine stamps) and they have two limited edition stamps available just for Tanabata (see their website for the designs each year).
The Tanabata festival at Kamishinmei-tenso Shrine is a smaller and more local-feeling festival, and they even light up the trees after 8PM when it gets dark (see their website for photos). Note: There are no food stalls here like some of the bigger festivals.
Many events are held throughout the year at this shrine located in central Tokyo. It's a popular destination so expect large crowds. Note: There are no food stalls like there are at other Tanabata festivals.
Tanashi Shrine is located in Nishi Tokyo, and hosts many different events over the year throughout each season. During rainy season they install a "Teru Teru Bozu Tunnel" where you can buy a teru teru bozu, and write a wish on the paper attached to it for Tanabata.
Teru teru bozu are small handmade dolls that resemble ghosts (unintentionally), and are made of cloth or paper that are hung outside in various places to bring good weather and prevent rainy days. It is said that they were first created by Japanese farmers, and then became popular amongst urban dwellers during the Edo period.
Great resource!