My doctor is a PCOS specialist. The first thing she does with all her patients is put them on low-carb. Most of us have insulin resistance, so following along with what works for a diabetic diet makes sense.

Here's a rather depressing study about PCOS and caloric needs to drop bodyfat.

What's hands down worked the best for me is Lyle McDonald's Rapid Fat Loss. It's a protein sparing modified fast and is a rather serious way to go - you're eating few enough calories that you actually have to start supplementing things like potassium to stay healthy. I followed it for 3 weeks, which is as long as I'm willing to eat 1,300 calories a day. I did manage to both gain strength and lose weight on this diet, something that I'd never had happen before. It's boring, it's hard to go out to eat more than once or twice a week, but you aren't really hungry because you can eat all the green veggies you want.