Why Am I Not Losing Weight?

Okay, so my New Year's resolution for 2010 was to eat healthy and exercise and get to a healthy weight. I remained faithful in my resolution, and by the end of the year I had gone from 275 lbs to 235 lbs (a net loss of 40). I am a 24 year old male, and I haven't lost a single pound since Christmas. I figured I would plateau eventually, and I've changed up my workout regimen since then, as well as starting Weight Watchers, but to no avail. I went from hour-long sessions on the treadmill, stationary bike and elliptical 4-5 nights a week to 30-minute sessions on them with higher intensity intervals for 2-3 nights a week. Again, nothing has changed. Now, I know muscle training helps speed up my metabolism and the fat-burning process, but I'm still a doughy tub of lard and don't want to make myself bigger just yet. What should I do/be doing?