How can I overcome a weightloss plateau?

I started losing weight about nine months ago. I started out at quite a high weight but have so far lost 120 pounds. I would like to lose another 50 or so but I have been stuck at the same weight for about a month now. I have increased my cardio to 50 minutets 3-4 times a week and my calorie intake is anywhere from 1000-1200 a day. Any tips for getting my metabolism to kick back into gear?