Frankly, this is probably the best Angelia Jolie has looked in years. I agree with Ingram that she was extremely underweight prior to her pregnancy, so the added body fat that she put on as a result of being pregnant actually made her look healthier post-delivery.
So I'm not sure that she's actually lost that much post-pregnancy weight -- she just had very little to start with prior to pregnancy, so her current weight is probably much closer to the healthy weight of someone of her height.
Also, the idea that Angelina is a fitness buff and works out a lot is actually a myth. She looked fantastic in the Tomb Raider movies, but behind the scenes complained about the amount of work and time in the gym she had to spend to get those great muscles and athletic look. This was a major reason why she opted not to do the third Tomb Raider movie -- she didn't want to do the physical training required to get that buffed look.
Emma, if you've recently been pregnant and are trying to lose some of the body fat you put on, the best approach is to adopt a clean eating approach to your diet and incorporate regular exercise, including weight or resistance training coupled with some cardio.
I know this sounds really basic and rote, but it IS effective. In fact, it's the only real way to shape your body. A great example is Jessica Simpson, who looked fantastic (in my opinion) in the god-awful remake of The Dukes of Hazzard. To get that lean, taut, muscular bikini body she sported in the movie, she spent hours with a personal trainer lifting weights and running. She also had very clean meals fixed for her, with a good balance of complex carbs, healthy fats and lean proteins.
In other words, you can't get that look with diet pills or magic teas. It takes WORK and commitment.