Michael Ende used to be one of my favourite authors as a kid, but I only started to realize how much I love his books when I reread The Neverending Story a few years ago. They seem to be simple children’s stories when you're young, and they work on that level very well, but they also have real depth to them that you become aware of as you get older. If your looking for art-inspirations, most of his books have pretty good illustrations, his writing is very visual and his worlds are filled with all sorts of weird creatures, locations and concepts.
Here's his books in no particular order:
Momo - A little girl goes up against an evil organisation that's out to take her friends away. The theme of this story is time and how, when we try to save as much of it and live as efficiently as possible, we seem to have less and less of it.
Night of Wishes - This one takes place on a Sylvester evening and it's written in such a way that you can read it in real time, which I think is pretty cool. A cat and a raven are trying to stop wizards from polluting the environment. It's a little on the nose but other than that I like it.
The Neverending Story - Explores the nature of fiction and reality by telling the story of a boy reading a book and losing himself in its world. Not sure how to get into more detail on this one without spoiling the fun. If you think you know what it's about because you've seen the movie and have no intention of reading it here's an article
that breaks it down pretty well.
Jim Button - A series of children’s books. Yup, that's it. You'll still enjoy them if you're into road trip adventures.
Mirror in the Mirror - A collection of shortstories that are connected with each other in subtle ways. The individual stories are very different in nature, but feature some of the same characters playing different roles, though it's never stated how everything fits together and you have to try and figure things out yourself. I think this i's Endes best book along with The Neverending Story, but it didn't get a lot of recognition because people thought, and still think of him as a children’s book author.
Prison of Freedom - Another shortstory collection. No interconnected structure in this one, but it's still pretty good. I don't think it was translated though.
There's two collections of observations, thoughts and story ideas that Ende wrote down over the course of his life. These weren't translated either, but if you know German they're definitely worth your time, and he also wrote a few plays which I haven't read.