Hi,
From Aix en Provence you can easily go to Marseille where there are some very good schools, for example the Studio Collette Armand. They producted some vety good dancers.
Here is their website
www.studioballet.com
As Estelle said, Aix is a very nice city as well Nantes, but if you don't like a rainy weather, you have to go to Aix. Paris is also a very nice city. One of my american came once a semester, then for one year, and finally she visits Paris each year now.
Please feel free to P/ ot e-mail me if you want more informations