I take belly dance lessons with the Goddess Dancing (www.thegoddessdancing.com) in Cambridge, and I really recommend them if you are looking for a supportive environment. It is easy to criticize them as being too spiritual and insufficiently critical in their approach, but I was not a confident dancer when I started and the instructors completely sold me on becoming a belly dancer. They sincerely believe that every woman is special and every woman can achieve in this art form, and they are willing to adjust classes somewhat (especially the beginner classes) based on what works best for their students or what their students are interested in learning. And I can definitely do things with my body that I couldn't before.

With that said, if you are an experienced belly dancer, you might want to meet with one of the teachers and discuss your learning needs instead of signing up for a class, as private lessons might suit you better.