As for the Protestants, their important monuments are in Eastern France (Metz, Montbeliard, Strasbourg), due to evident reasons.
Here is the "Temple Saint-Martin" in Montbeliard (once a free Imperial Lutherian city in Franche-Comté) :
Here is the Temple Neuf, constructed in Metz by the Kaiser in 1904 for his officers :
In Strasbourg, the "Eglise Saint-Thomas" :
There is a lot of small and splendid small Protestant churches in Alsace and especially in Strasbourg, but I would need another thread to post all their pictures...
Also, Strasbourg's cathedral was a Protestant temple between 1521 (Reform) and 1681 (French annexation).