Tamagotchi Colour - simple and not too needy, but possibly expensive. Look on eBay for this one.
iD - more features and less needy than Colour. Can be expensive. Look on eBay for this one.
iD L - almost the same as the iD, but new features, characters or games. Not too expensive. Look on eBay.
Ps - almost the same as the iD L, but lots more features, characters and games. Look on CD Japan or HobbyLink Japan.