Look for a Wellness Centre in your area. They are usually well rounded with something for everyone and usually membership includes classes such as aerobics, aquafit, yoga and stretch.
You could also check out the YMCA.
I looked into Curves but decided against it because it seemed very expensive for what you got. Because of physical limitations with my right ankle and left foot, I wouldn't be able to do a few of the machines. I really need cardio but they don't have a treadmill, and all of their equipment is "manual" which would put undo stress on my joints and because I get short of breath with exertion, I wouldn't get the proper work out. So I go to one of our local Wellness Centres.