I have mentioned them before -actually, I have mentioned the mascot Hani-maru (はに丸) that exists to bring children closer to them. But Haniwa (埴輪) figures, made of clay during the period between the 3rd and the 6th century are one of the most interesting chapters of ancient Japanese history. In the following pictures, you can see some of the pieces of the respective collection in Tokyo National Museum -these figures have been found in various burial mounds (aka "kofun"/古墳) and are characteristic of the period with the same name (250-538).
The last picture is the "Warrior in Keiko Type Armor" (keiko no bujin/挂甲の武人) one of the best examples in terms of construction technique and detail and was found in Gunma Prefecture's Ota. It is considered a National Treasure of Japan (and justifiably so, I think) although some of the other figures are equally good.
(For a bigger version of these pictures both in color and black and white, check my "Japan Arekore" set on Flickr)