In the past year, they've released the FamiTama, Royal FamiTama, and the Tamagotchi Plus Color. The FamiTama models are similar to the regular V5 & V5 Celebrity. The Tamagotchi Plus Color is unique.
Here's a list of major releases
Release date - main models
YYYY/MM/DD
2004/03/20 Tamagotchi Plus - equivalent to Tamagotchi Connection V1
2004/11/23 KeiTama - sort of like a V3, but without a TamaTown web site
2005/07/23 KeiTama Akai-series - a red-screen version of the KeiTama. Different characters & games.
2005/11/23 EnTama - sort of like the V4
2006/07/22 UraTama - a blue-screen version of the EnTama. Different characters & games.
2006/11/23 TamaSuku - instead of taking care of a virtual pet, you're taking care of a school class.
2006/12/09 EnTama CYOI - a refresh of the EnTama - same characters, different games.
2007/02/24 TamaSuku 2 - different class subjects
2007/11/23 FamiTama - equivalent to the Tamagotchi Connection V5
2008/03/29 Royal FamiTama - equivalent to the V5 Celebrity (V5.5)
2008/11/22 Tamagotchi Plus Color - a color-screen Tamagotchi
Other models with characters you can raise
Hanerutchi - similar to a KeiTama, but characters are based on a Japanese comedy troupe
Hanerutchi 2 - similar to an EnTama, but characters are based on a Japanese comedy troupe
Tamago-chu - the "kissing Tamagotchis", sold in a pair, aimed at a more mature market
Oden-kun Tamagotchi - similar to the Tamagotchi Plus, but characters are based on the Oden-kun cartoon in Japan.
For pictures of each, visit Bandai's Japanese products page, here:
https://tamagotch.channel.or.jp/item1/toy/index_1.html