During the month of December 2010 the Espace Saint-Louis, Saint-Paul, Villiers and Madeleine are offering 3 free classes to non-members. There are 15 classes to choose from including Hatha and Ashtanga Yoga, Pilates, Feldenkrais, Oriental, Jazz and Latin dance. Sign up here in French.
Side note: This is one of the few centers that is completely internet accessible. Membership, course schedules, sign-ups and even annulations can all be managed on-line. This is one giant leap for the web in France.