First off, much admiration for the work you have done so far! Shedding 50 lbs. is quite a feat in and of itself.
There has been a lot of good advice here. Please allow me to chip in a bit.
Weight lifting
You have to do this to burn the lbs. As mentioned earlier, increasing muscle will speed up your metabolism which will in turn burn more of what you don't want. All those ab excersises are included here, but don't forget the basics, i.e., bench press, squats, leg raises, curls, leg curls, etc. etc. Work the big muscles first (pecs, quads etc.) followed by the smaller muscles (Biceps, Triceps, Calves etc.) If possible, do three days a week, Day one, Push excersises like bench press, incline press, overhead dumbell press etc, Day 2 Pull excersises like seated rows, lat pull downs, curls, shoulder shrugs, etc and Day 3 legs, squats, leg raises, lunges etc.
Running
I have found basic jogging to be too hard on the joints, all the joints, from the obvious (knees, ankles, back, etc.) to the not so obvious (shoulders, even your jaw.) I prefer running up stairs (much less impact and much more difficult) while walking down.
Swimming
If you have access to a pool, this is the best overall cardio-vascular workout you can get.
Diet
Becuase of the workout your muscles are getting, get plenty of protein in your diet (Chicken, Salmon, Tuna, Lean Beef, pork loin, egg whites (i like to mix 4 eggs minus 3 yolks for my scrambled eggs) 2% milk). Try to get .8 grams of protein for every pound of your target weight. Don't cut out dairy! Dairy products contain Casein, which helps to burn fat (unless you are lactose intolerant, in which case you should avoid casein like the plague). Lowfat yogurt is great. Eating 1/2 a cup of lowfat cottage cheese at night just before going to bed helps deter atrophied (sp?) and causes the body to burn off fat instead of muscle while you sleep. With all the protein in your diet, drink plenty of water. Shoot for 1/2 a gallon a day. Lots of fruits and vegatbles. Asparagus, Tomatoes, Spinach, Boc Choy, and brocolli are fantastic.
Sorry for the length. Just trying to help. This regimen works for me. I'm 34, 6'0" weigh 180 lbs, I have a resting heart rate anywhere from 45 to 50 beats per minute and somewhere between 7% and 9% body fat. Oh, and I'm very happy with the results. I can bench press nearly twice my weight. And the wife loves the guns.