The only way to do it and make it stick is through diet and exercise. You need to decrease your caloric intake (number of calories you eat) and increase your output (exercise more) the more cardio you do (such as running) the more weight you will lose.
Start with cutting out/back on sweets and heavy carbohydrates. You can still eat carbs, just in moderation. If you lose weight fast, with pills or something like that you are not teaching your body and changing your lifestyle so that you can continue with it. Once you change your habits you can continue them :)
The best way to lose weight would of course be the all natural way. Eating healthy foods low in starch and staying away from the junk food. Also by drinking plenty of water and really practicing self control. To keep the weight off, continue to practice good eating habits. With the way things are being recalled today such as diet pills & supplements, this is the best all natural way.
To lose weight: eat less calories than you burn in a day. If you want to do this in a healthy way, then reduce your caloric intake just a little bit each and everyday. There is this really great tool that I've used to monitor my calories and exercise regime: http://www.freedieting.com/tools/calorie_calculator.htm
Here is essentially what you need to do.
1) Find out how many calories you should be eating a day for your weight and height. 2) Figure out how many calories any exercise you do will burn. 3) Use the advanced options to see the 7-day-calorie cycle (its essentially a way to trick your body into always losing weight -- you change the amount of calories you eat everyday -- up and down). 4) Keep track of what you eat so that you can meet your daily goal. 5) Once you've lost a significant amount of weight, lets say every 5 pounds, you're going to have to recalculate *you'll end up having to either eat less calories or burn more through exercise as you lose more weight*