Thanks, last10lbs and everyone, for the advice. It looks like I have entered starvation mode. I've begrudgingly decided to stop losing weight and work on maintaining weight while increasing my caloric intake. My next goal is to be able to eat ~1500 calories per day while not gaining weight. Then I plan to go back on the diet (500-1000 calories per day) but only for a couple weeks before easing back up to 1500 again. I'll repeat this until I hit my goal weight. After that, it would be ideal to be able to eat 2000 cal/day without gaining weight, but we'll see.

I think my mistake was following my diet for too long. If I stopped after 1-2 months I would have been fine, but I guess I've learned my lesson. At least now I know how to drop a quick 10-20 pounds in the future, should the need arise.

The terminology makes it sound bad -- I wouldn't call it a 'cheat' day because I didn't crave those bad foods. I have been perfectly happy on my new healthy diet. To some extent I think 'cheating' did help me. There was always a meal or two that I couldn't avoid for social reasons, namely going out to eat. I used to groan at those, thinking about how much they would offset all my hard work, but in retrospect I think they kept my metabolism from falling into starvation mode even earlier.

As far as keeping the weight off via lifestyle change, I think I am all set there. I used to envision the smorgasbord to which I'd treat myself upon reaching my goal weight, but now the thought of all those foods makes me queasy. I really like the fresh foods and I enjoy cooking -- I'll gladly ditch those Hot Pockets in favor of a nice chicken curry or a freshly-pealed orange. I've learned that I can put the fork down before I feel full and I'll still be satisfied until the next meal. I've found other things to do when I'm bored besides eating. The same sentiments go for exercising.