HoMM VII Haven Units – Haven faction units from the seventh installment of Heroes of Might and Magic.

This is a very well-known mod about a pirate town. Horn of the Abyss. Just Google it.

Added 6 minutes later
And for some less well-known mods for the third game, they created models and animations. I remember there was a mod with a dark version of the human castle, with inquisitor executioners and dog handlers or something like that. There were also new models created from scratch. But the fifth game didn't get that. Of course, the models in the fifth game are more complex than in the third.