This temporary stand-up sake bar is back again this year, run by a sake brewers' association and showcasing premium sake from 66 different breweries around the country. One improvement over last year is that it will run for 9 months (through October 2007) instead of only 10 weeks. They've also made it a little easier to find your favorite sake - in addition to the Japanese-only menu there's a wall display of all 66 bottles that they regularly carry.
Sake is Y300 or Y400 per tasting-size glass, which you pay for from sheets of tickets that you get at the counter (Y1000 for eleven Y100 tickets). There's a very limited food menu of odd little sake snacks (my Y500 platter had wild-boar ham, kamaboko fishcake and pickles), but it's probably a good idea to eat something more substantial before you start in on the sake.
Kura 66 is kind of hard to find; it's located next to a couple of ramen shops, on the B1 level underneath the Yaesu South Exit of Tokyo station. The bar's website (www.ginjyoshu.jp/bar.html) has a coupon for a free drink, and there's also a map which you might be able to show to someone if you get lost.