With many thanks to Jason Kottke for the recommendation, I just finished enjoying a lovely pain au chocolat from Boulangerie Malineau in the Marais about five blocks from me. Crisp, nicely layered, and warm, just a bit too buttery. A superior pastry, even for Paris.
One wonderful thing about Paris is the diversity of bakeries, cheese stores, butchers, etc. Everyone seems to have specific favourites; this place is good for pain ordinaire, this one for croissant, this one is more convenient. So much to learn.