I started (a few weeks ago) working out with some friends, and it is the only thing that has been working for me since having children. Every morning (M-F) at 9 a.m. I pack up myself and the kids and we go to my friend's house. Another friend meets us there with her youngest. The kids (between the three of us there are 6 kids usually, sometimes more when one of us is watching someone else's kids!) all play together or watch a movie in an adjoining room, and we do some kind of workout video or EA Sports (I think that's what it's called? Might be EA Active or EA Fitness, can't remember) on the Wii. I don't have a Wii or any of the necessary gear (thigh strap and nunchucks) so I just follow along without being monitored. Or we do some other workout. We've been doing a lot of Jillian Michaels' No More Trouble Zones lately, and that one is a killer (for me anyway, since I am really out of shape).
But it is great because meeting up with two other women keeps me accountable so I work out even when I don't want to. I know they are expecting me, so that gets us out the door every morning at 9, no matter what. I need that, or it is too easy for me to justify myself out of it, like I have in the past. And the kids just play and have a great time (for the most part. Occasionally my baby will get in my way while I am trying to exercise but it is still the best system I have found so far.). My son looks forward to it every day and has major meltdowns when we can't make it for some reason...
I am also doing the Couch to 5K program on my own (3 days a week after working out as I already mentioned), just because I have never liked running and I want to. I just started that this week. I am doing it M, W, and F when we get home from exercising. I put my baby down for a nap and my preschooler watches a show while I run on our treadmill.
I am also going to start some classes in the evenings, once or twice a week. I used to dance (through high school and college) and I miss it, so I am looking at doing a Zumba class (for fitness) and a ballet or hip-hop class (for fun).
When the weather warms up, we do a lot of hiking and cycling, but I don't do either one consistently enough or hard enough to lose all the weight I want to and to firm up my muscles like I want to. But it helps at least keep me healthy and helps me maintain my weight, even though it doesn't help enough with weight loss.