hi bradamant, i see you've found the fnac already, to add to the other suggestions already given, there are a few other french ebookstores, take a look in the french forum for a few threads discussing / listing them. the selection of recent (non pd) books is still woefully small (not nearly comparable to english language ebooks) but little by little it's getting better, and new publishers concentrating specifically on ebooks are appearing.
also, on feedbooks.com there is french, english and spanish available ; a lot of pd, but also a lot of contemporary authors releasing their work under a cc licence. recently, paolo coelho added his work, in fact.
hopefully you'll find what you're looking for !