Sushi Hiro, Acton. Seconded strongly! The atmosphere is cafeteria, but the quality and prices are great! Also, when in Acton.. there are a couple of good Japanese grocers. One is just down the street from Sushi Hiro, the other is.. eep, can't remember. Close to a train station.
Tosa is pretty good, but a bit pricey for izakaya food.