Eilonwy (peas in a ).
Probably one of the most currently underrated classic children's authors I can think of is Lloyd Alexander. He wrote a bunch of books that were pretty good, but his pinnacle was the five-book Prydain Chronicles and the (for older readers) Westmark trilogy.
Delicious blends of high fantasy and adventure, comedy, sometimes dark and provoking themes, and a love of Welsh mythology and Dickens-channeling characters have kept him high on my bookshelf ever since I first read him many decades ago. So good.
Also, I love a decent mystery and enjoyed the one John Green I've finished so far. One lifetime for so many books...