There's a brand-new restaurant complex that just opened in November in front of Ryogoku station called Edo Noren, and among the shops there's a very unusual standing sake bar called Tokyo Shoten. The first unusual feature is that all the sake is dispensed from vending machines - thirty different types of sake in total. (I've seen similar setups in Niigata and Yamagata but never before in Tokyo.)
More unusual though is that all thirty kinds of sake are made in Tokyo. I didn't even know there were more than one or two breweries within the city limits, but apparently there are several. Small-size tasters (40ml) are Y300 each, and there are tiny salty snacks for Y100 each. It can get crowded, but since it's a standing bar there's pretty rapid turnover.