I posted this on another forum for someone who was stuck on a plateau but thought it may be helpful here as well. Hope it proves useful to someone!
Several years ago I worked with a trainer and when I would hit a plateau I would hit them harder than anyone she had ever worked with so I feel your pain. She said the only way to get through one is to do one or more of three things-- increase your intensity, your duration or your frequency. I hated her a little for it but it always worked. So, for example, if you are doing 30 minutes (duration) of exercise once a day (frequency) you may want to up it to 45 minutes twice a day until you break through. Or you could increase the intensity and step up the incline on a treadmill, up the resistance on an elliptical or increase your heart rate by 10 beats a minute. I would have to do two one hour exercise sessions to get through some of mine... thus the hating her just a little.
She also always encouraged me to vary my exercise so my body didn't get used to doing the same thing. So one day walking, one day elliptical etc.
She said you can expect to plateau every 10% of your body weight that you lose but can preempt it by doing the above things. That also helped, I skipped a couple plateaus that way.