Nihonshu Stand Moto is a very informal bar that specializes in nihonshu, in this case quite a good selection of it at reasonable prices. The food menu is more extensive than you'd expect, dominated by small sake-friendly dishes like smoked mackerel and fried oysters. Open from noon on weekends. (Note that there's a small Y300 table charge.)
This book will introduce you to more than twenty of Japan's favorite specialty foods that are less well known abroad, along with a guide to the best places in Tokyo to try them and expert tips on what to order. From Bento.com.