Chao
Here are some images of my Chao in-game. He has that evil smile because I tried to kill it once because my other chao, Swooby, died when I paid more attention to Uchao. So I got pissed and tried to kill Uchao. That aside, he's forgiven me, but since I did that when he was young, he retains his aggression (hence the evil smile).
Here's some pics of Uchao (forgive the quality, frame saves of a screened video with my camera).



You can also take your Chao from the game, and put it on the VMU (visual memory unit). That is Dreamcast's memory card, but with a screen and buttons, kinda like an old school Gameboy, but smaller and cooler.
Here is some stuff on the VMU.