I don't know what genres you like or if you read classics, but many of my favourite authors are French:
Alexandre Dumas (
The Three Musketeers, The Count of Monte Christo, ++)
Marcel Proust (
In Search of Lost Time [alt.
Remembrance of Things Past], a novel in seven volumes)
Jules Verne (
Twenty Thousand Leagues Under the Sea, Journey to the Center of the Earth, ++)
Anatole France (
The Crime of Sylvestre Bonnard, The Gods Are Thirsty, ++)
Victor Hugo (
Les Misérables, The Hunchback of Notre-Dame, Toilers of the Sea, ++)
Gustave Flaubert (
Madame Bovary, Salammbô, ++)
Pascal Quignard (
All the Mornings of the World)
Marquis de Sade [Donatien Alphonse François] ("
Justine; or Good Conduct Well-Chastised", "
Juliette, or Vice Amply Rewarded", "
The Crimes of Love: Heroic and Tragic Tales", ++)
Émile Zola (
The Mysteries of Marseilles, Germinal, The Joy of Living, ++)
Guy de Maupassant ("
Bel Ami, or, The History of a Scoundrel" and a vast number of short stories)
Jean Cocteau (
Les Enfants Terribles/The Holy Terrors)
I've read all in English or Norwegian translation, since my French is limited more or less to asking the time and ordering beer. They'll be better in the original language of course, but even in translation these are all truly excellent books. In my opinion of course.