Zumba is a fantastic aerobic workout that feels much more like a great dance party than your typical aerobic workout. It's dance based with great salsa, samba, reggae and other international moves. It burns a ton of calories! I find it doesn't feel at all like exercise to me and I actually look forward to going. I've only been going for about a month or so now so I haven't noticed any toning yet, but all the hip and stomach moves have to be doing some good.
I prefer the classes at my local gym. I bought the dvd set from their website recently so I could do it on the days there are no classes going on at the gym. They are still good, but I don't push myself as hard when I'm by myself. I also need to start doing it in the kitchen because I nearly wretched out my knee on the carpet with my running shoes.