I love Weight Watchers! I've been on it a few times in the past, and I'm on it now to drop the baby weight (and then some!). Like someone else said, you can totally do WW while breastfeeding.
The thing I love most about WW is that it's in no way a "diet". It's a lifestyle. It teaches you how much you should be eating, and how to give and take instead of just having whatever you like. I think of points as money, and you just have to budget. It's like, you can have that cheesecake, but it's going to cost you more.
And it's possible to lose weight without being super active...as long and you track and follow the program, you will see results. The first week I didn't exercise at all and I lost 2.4 lbs! And with WW, you stay on the program even once you reach your goal, and you can become a "lifetime member", which means that as long as you're within 5 lbs (I think?) of your goal weight, you can attend meetings for free.
There's a great WW thread in the Dieting, Weight loss, and Fitness forum.