This long-established unagi specialist (since 1894) serves excellent eel in a thick, somewhat spicy sauce. Prices are very reasonable: unaju (eel over rice) from Y2100, full-course menus Y4200-9450. Be prepared to wait awhile, as eels are prepared from scratch. They also have a branch in Matsuya Department Store in Ginza (03-3567-1378).
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.