Jughead is correct, strength training is important for long-term weight management, and reduces injuries and aches&pains if you are older.
The best way to lose (and keep it off) is a long-term lifestyle plan which is SUSTAINANBLE. More than one way to go about it, but these are the basics...
Reasonable cardio 30-60 min 4-6 times/week
Strength training, enough to build some muscle mass
High protein diet with fruits, veggies, fewer carbs, and less fat/dairy. Quality carbs only...oatmeal, whole grain, etc. Don't eliminate dairy & fat, but do cut back if you are currently overboard with it.
Probably most important: eliminate all crap processed food and I pretty much mean all. Don't eat anything which can be found in a mini-mart or the ATL airport...think whole foods or the budget equivalent. OK I eat a bag of peanut M&M's occasionally but that's it (and I do serious cardio)
Ease into it somewhat gradually, the exercise will feel good before long and you'll crave it. If you are not used to much exercise, ramp up slowly for 2-3 weeks then take one week off (this is VERY important, otherwise injuries are guaranteed unless you are very young). Your food cravings will diminish as your body adapts to the exercise (unless you are doing extreme endurance training). Even the fruits and vegies will taste pretty good after a while.
Once you get some muscle tone and body fat under 20% then look at PX90 or other extreme fitness systems if you feel the need. Otherwise you'll probably hurt yourself.