In reply to exploringtim:
It seems you have enough suggestions for a first visit! One for another is Mont Aiguille near Fontainebleau town. There are several circuits, yellow, orange and blue IIRC and they seem to be a bit less polished than some places, except the start of the yellow and orange.
As for the choice of circuit, the best is to have a few ideas in mind and then decide according to the weather - if it's hot, and it can get really hot in Summer, go for a spot under trees, if it's damp but clearing up then an exposed area - like the Cul de Chien - dries quicker.
Concerning the "Bilboquet" dog's head boulder, it has been out of bounds for climbing for a long time as it's a landmark, but a delicate one. It's no great loss for climbing though as it's only small and surrounded by about the biggest climbing area in the forest! Putting a fence round it would spoil the appearance of the place, and the thousands of photos - a good rendez-vous spot though and nice and sandy for children.