I used to weigh 260 lbs, and I've gotten down to 192 over a couple years. It's all about changing your lifestyle. I eliminated all fast food, and I also eliminated 3 things from my diet entirely.
High-fructose corn syrup, refined white flour, and hydrogenated oils a.k.a. Trans fats.
If you get rid of those three things, you're more or less eating healthy by default. Also, trying to switch your snacking habits from more processed foods to more raw and natural foods works well too.
Also, read the nutrition labels! The FDA states that if there's less than .5g of trans fats per serving, a company is allowed to say it's trans fat free. This means that instead of getting rid of trans fats, companies can just shrink the serving size. Look at the ingredients, if it says hydrogenated- or partially-hydrogenated oils, keep away! In addition, if you actually look at how many calories some foods have for a rather small portion, you'll think twice about eating it.
Using these few tricks, I'm actually eating MORE food, yet significantly fewer calories overall.
Also, going for a walk or lifting some weights occasionally works as well. I have a little program going that works pretty well for me. 3 days a week (usually Monday, Wednesday, Friday

Every time I get up out of my chair to get a drink/use the restroom/whatever, I do:
25 jumping jacks, 10 squats (body weight), 10 push-ups or 10 inverted rows (alternate them, you don't want to push more than you pull, or vice versa. it'll cause problems,) and 10 crunches. do this as fast as you can, while still practicing proper form. It's both cardio and weights, and your heart is racing afterwards. It only takes a few minutes, so it doesn't feel like you're working too much, even if you do this several times a day. I give myself a day between these to rest and recuperate, which is as important as the workout itself.