I’ve recently come back from France, and once again been puzzled by many place names. They just don’t correspond to any spelling conventions in the everyday vocabulary, and yet the French give us no help: to the best of my knowledge, there is no pronouncing dictionary that includes place names (or family names). The Petit Robert has two appendices – “Adjectifs et noms tirés des noms propres” and “Dérivés des noms de personnes (réelles, mythologiques, imaginaires)” which are very usfeul, except that they give no help with pronunciation.
Even the French are often confused by the pronunciation of place names. Perhaps the most famous difficulty for them is Chamonix, which French friends have told me they used to pronounce /ʃamoniks/ – until they went there, and discovered that locals call it /ʃamoni/.
In no particular order:
Eawy, Bulgnéville, Thueyts, Andernos (-s silent or pronounced?), Villers (several places of this name – /vije, vile, vilɛr/?), anywhere ending in -x (silent or pronounced?)