I'm from the UK and someone has already given some good suggestions. So instead I'll recommend some French authors that I really love:

Alexander Dumas - if you want a great adventure. I can't recommend the The Count of Monte Cristo enough. It's an epic tale of revenge. Victor Hugo - for something that will make you question your morals. Les Misérables is a classic and has some incredible moral dilemmas. Jules Verne - Fun stories of early science fiction. 20 thousand leagues under the sea is an enjoyable journey with a surprising amount of science.