Here is a very in-depth, no-nonsense approach to overcoming a plateau:
http://www.answerfitness.com/208/weight-loss-plateau-tactics-overcoming-weight-loss-plateau/
It recommends everything from changing your exercising routine to calorie cycling. It's a great article and offers several different paths to breaking the plateau.
Have you figured out your BMR and total calories burned and then adjusted it as you have lost weight? If not here is a website you can do so:
http://www.goodhousekeeping.com/health/advice/calculate-calories-bmr
Go by that and also maybe up your exercise. That's all I know to tell you...hope it helped some! Good luck!