I sort of like Moaning Myrtle. She was one of my favorite characters in her brief scenes in the second movie. I fell in love with her voice. I dont what the actress sounds like in person but she really does a good job. And in GOF she not only does the voice again perfectly, but she adds a lot of comedy to the bath scene. And if you think about it, some scenes you dont want to go and im very glad the directors and screen writers kept her in both those movies.
If you reply, you might want to include, smaller actors like my example or all movie actors like the 3 main characters etc.