I lost about 40 lbs after having my daughter, which was 20 lbs past my prepregnancy weight, but most of my weight loss was because I was depressed and not eating enough. That said, I've managed to maintain that size for the last two years through portion size control and an active lifestyle. I serve my food on small plates and try not to eat too many things that are really fattening-- fried, creamy, tons of processed sugar, etc.
I also try to snack in small bowls rather than bringing in the whole container to eat out of. I mean, I fail sometimes-- earlier this week, I ate an entire family sized bag of Ruffles in one sitting. I freaking LOVE potato chips-- they're one of my major weaknesses. But that's also why I don't keep that stuff in my house. But alas, my Mom does and that's where I am right now, so...binge snacking sets in.
But yeah. Portion size and then also, my husband and I go hiking a few times per week, we go geocaching, I generally do calisthenics a few times per week, and I'm constantly chasing around a toddler. So by coupling portion size with an active lifestyle, I've been able to maintain my body at half my previous dress size. Plus I don't feel like I'm "missing out" because I still eat delicious stuff, just in small portions. It's what I've found I can maintain long-term.