The next books in french I’m going to read are the Arséne Lupin series. I already finished Arséne Lupin, the Gentleman Burglar, which was pretty good. I first got interested after reading Phantomas. These books were the french answer to Sherlock Holmes but written from the point of view of the criminal. I found the whole collection very cheap on ebay.
I’ve seen a couple of recent film adaptations of some of these books. Apparently they’re not as good as some earlier films but I wouldn’t know!