For me, the best way I found to lose weight and keep it off was to become serious about my running. I find that by doing so it has changed the way I think with regards to food.
I tried running on my own for a while but I would drift in and out for weeks at a time. Sometimes I'd be at the gym daily, other times I would miss a whole week. I found I could never get any balance regarding exercise.
I decided to join 2 running clubs. One goes out on a Tuesday and Thursday, the other on a Wednesday. At first it was difficult as I was out of shape and carrying too much weight. I also entered races I found on this site - so far I've done 10k, 10 mile and half marathon. Tomorrow I have a 10 mile race but now I have a time to beat from my first one. I'm about 2 stone lighter from the last 3 months training and a lot faster and fitter than when I first started out. I expect to knock about 10 mins off the last time I did based on the times I've been getting in training since my first 10 miler. I haven't gone on a diet I just know that to keep improving in my running (which I'm enjoying) I need to carry less weight and eat foods that will give me the energy I require. I did some research on what to eat and what not to and 90% of my diet is healthy. Plenty of water, fruit and salad. I do still eat things like chocolate etc because let's face it, I'm not going to never have chocolate again in my life. But I wouldn't make myself sick with it as I know being lighter will get me faster times.
By the way, I'm never going to win a race I am just competing against myself. I'm looking forward to the run tomorrow to see how much I've improved since starting out.