In the lore, it says that there have been rumours of Werelions (Kahjiit) and Werecrocs (Argonians).

There were Werebears added in Dragonborn, so I'm kinda wondering if there are any mods for this?

Moonlight Tales - http://skyrim.nexusmods.com/mods/35470//?

Both adds werebear NPCs to Skyrim and allows the player to become one.