wanted to second (or third?) the jogging stroller. have one and use it at least 2X a week, it really is fun to jog with and even if we're just walking. Its a much smoother ride than using our regular stroller that makes her teeth chatter since our neighborhood is kinda rural and there are no sidewalks, just asphalt.
Also wanted to recommend zumba if you like dancing, I don't go to classes (though I hear they are great) just use a workout dvd and it is very fun. I've lost weight doing both of these things, and the zumba in particular is really good for working out the hips/midsection since all you do is shake your booty Plus, LO loves to watch and try to dance too its pretty cute.