Bouillabaisse in Provence (not necessarily Marseilles)
Cassis & Bandol beach areas a good bet. My information is out of date as to specific restaurants.
A good tip is to look for a smaller place that says they require 24 hour notice to do bouillabaisse. Normally you get a quality dish that way.
We found a place like that (just West of Bandol) and had by far the best we've ever had.