Standing (Score 1)

There are already several intelligent posts here, about increasing activity and decreasing caloric intake. Read The Hacker's Diet for a good engineering perspective on the ins and outs (as it were).

You have a problem of insufficient activity to burn calories. I had the same problem, which has been solved by A) going to the gym, and B) standing while I work. I think the latter point here can really help you.

If you can wrangle your work space around to allow you to stand -- either by piling your computer on top of additional shelving, say -- you can burn an extra 60 calories an hour. And more, if you take that additional standing time and throw in extra movements during your work day. When standing, it's easy to just walk away for a minute, throw a ball up and down, heck, do some jumping jacks. When standing, you're that much closer to any kind of physical motion, and that has to be of help.

It's hard on your legs and knees at first, but you will build the muscles to support it. Good luck!

Cheers,
Aaron.