I'm a personal trainer and owned a local women's fitness studio. The best attended classes at our studio were Zumba and Yoga. Our Zumba instructor also teaches at 24 hour fitness.
Zumba is a great class - if you enjoy dancing to Latin beats/dances, this is a great way to lose weight. But watch out for back and joint injuries when you push beyond your limit. There are a lot of hip movements that could put some strain on your abs and lower back. The other posting is right, most people are sweating within 10 minutes. Some get lost learning the dance moves, but the important thing is to keep an open mind and have fun. It's okay if you don't know all the moves. Just do what you can. My business partner would rather dance her way to weight loss, which she did!
As for me, I lost my baby weight from post-partum yoga and power yoga. Let me know if you're interested. I can refer a great instructor.
C.