Recently, I read a fic by
lotesse called
Airy Cages Quelled. It was an AU of the fourth book in the Prydain series, Taran Wanderer, and it was basically the best thing ever. I've always loved that book (ymmv, but it's one of THE formative stories of my childhood), and in the fic,
lotesse turns the story on its head, and tells it from the perspective of the canonically absent heroine, letting her do the rescuing in a way that's... well, I'm not sure why the original story didn't tell it that way to begin with.
The books already have pretty good cover art, which will probably always be what I picture in my head for the characters, rather than say, the Disney versions, so I'm not really sure I'm doing the story or the character justice, but I was definitely inspired to try.
If you know the book though, you should definitely go
read the fic.