Favorite Animal Transformation

Well, before I like any transformation it should be done right. I've seen a few mangas, and also a couple of artists ( like Jollyjack ) who can do it the right way. A good story helps as well. As soon as it meets the previously mentioned demands:

I fail to be quite original but catgirl transformations are always cute. Sometimes just cat ears and a tail, sometimes a lot more, but it's all nice. Other then that, bovinian transformations are very cool as well.