Some of the larger
condo complexes have dance and yoga classes in their multipurpose rooms/function rooms. Typically an outside instructor will come in and conduct classes and you can either pay as you go or buy a package, depending on the instructor's policy.
Most
condos also have lap pools and gyms with things such as treadmills, elliptical trainers, stationary bikes, resistance machines and free weights.
If you're going to be living in a condo, you might first want to check out the facilities there before forking over extra money for a gym membership or signing up for classes that might involve a long commute.
Also, do you know what part of Singapore you're going to be living? It might help in making recommendations.