I've talked before about Tove Jansson, whose wonderful Moomin novels were a highlight of my childhood, and whose Moomin comic strips I'm now enjoying. When I was old enought to have my own credit card, I began (at what seemed to a student to be a great expense) tracking down those of her adult works that had been translated into English, especially The Summer Book, which is pretty much a perfect little novel, and Sun City.
A few years ago, Sort Of Books in Britain began republishing her adult work, beginning with The Summer Book and following it up with A Winter Book, which is a collection of short stories, and the novella/story collection Fair Play. They are all, of course, great. Esther Freud and Ali Smith have written introductions, available online, which ought to give you a good idea of why the books are worth your time.
Now, nice as those covers are, they don't use Tove's own artwork. For that, we turn to NYRB, who have just published an edition of The Summer Book that looks like this:
This uses Tove's own original cover art for the book:
She also did another cover, used on this Hutchinson edition from 1972.
The Summer Book is about a summer which a young girl, her father and her grandmother spend together on a small island in the Gulf of Finland. It's told from the girl' point of view. Tove had a look at the other end of life with Sun City, about the residents of a Florida retirement community. Not yet republished this century in English, the original cover, with Tove's artwork, looked like this.
Then there is the autobiographical Sculptor's Daughter, much of which is available in the two Sort Of collections. Tove's original cover for that is very nice indeed:
One book I have not been able to track down in English is The Listeners. The cover very much makes me want to read it:
Finally, here's a bonus illustration from a set Tove Jansson did for Alice in Wonderland.
Many of these covers came from The Moomin Trove, an excellent resource for finding out more about the various Jansson books. Lots of nice cover scans are to be found there.