Imagawayaki (今川焼き) is a round shaped sweet with sweet bean paste. The bean paste is made from Azuki beans (アズキ). Azuki beans are sometimes called red beans because of their color. A batter is made and poured into a small round pan. Then the bean paste is placed inside the round buns.
Taiyaki (たい焼き) is a snack in the shape of a sea bream. (A sea bream is a freshwater fish in Japan.) A mold is made in the likeness of a sea bream, and batter is baked in the mold. Then the sweet bean paste is used as filling.
Dorayaki (ドラ焼き) is a pancake like bun with sweet bean paste. The bun consists of two thin, round sponge cake pieces, with sweet bean paste on the inside. The paste is not spread out evenly, and the majority of it is in the center of the dorayaki. This is why the dorayaki tends to have a mound like shape.
Monaka (最中) is a wafer-like snack with sweet bean paste on the inside. The wafer-like buns are soft and easily melt in your mouth. Sometimes, the buns are not completely sealed, which gives you the option of taking out the bean paste and eating the buns by itself.
Anpan (あんパン) is basically sweet bean paste inside of a round piece of bread. Originally, red bean paste was only placed in sticky rice cakes because the Japanese were still new to bread baking. When rumors that the anpan was liked by the Emperor Meji (明治天皇) spread throughout Japan, the anpan became an instant hit.