Charlie and the Chocolate Factory, The Witches and Matilda for sure. The Witches is popular in Norway at least but I'm not so sure about other countries.

Charlie and it's not even close.

Charlie and the Chocolate Factory by far, but my personal favorite is Matilda.

Charlie and the Chocolate Factory, James and the Giant Peach, and Matilda

Same Matilda was one of my favorite books as a child

Charlie, but Matilda is the one that got me to read the rest of his books. When I found out there was a movie for The Witches I freaked.

The Witches is my personal favorite, but Charlie & The Chocolate Factory is probably his most famous. Then followed by icon Matilda and James And The Giant Peach.

The Witches
Charlie and the Chocolate Factory
Matilda

The trinity

Charlie and Matilda are my favorites, without a doubt.
And the movies are very good too (in Charlie's case, Tim Burton version is the best imo because it's more faithful to the book, despite the added plot line about Willy Wonka's father )

charlie and the chocolate factory obviously

Your taste