I've never really found any workout good enough - I've always had to diet as well, except when I played Rugby for a few months and that was amazing, but I was your age then. :-) Anyway, I would recommend high cardio and weights, but when you do weights, be sure to put them on a lighter setting and do more repetitions - this will burn more fat. I also recommend doing the random hill setting on the treadmill, if you have one that goes up and down to create an incline. This way you walk and jog and run or walk up hill a bit and sometimes on flat. It's a bit like interval training, which is also really good - this means you jog for three minutes and then either do a light jog or a fast walk for three minutes, alternating between the two. Helps me to keep from getting bored, too... As for the tummy area, I can't recommend the Tupler Technique more. This is a technique from Julie Tupler in New York that helps you lose inches from your tummy in a matter of weeks. This is especially good if you have muscle separation from being pregnant. I would not have believed the results if I had not seem them for myself. I took a workshop from Kelly and the Tummy Team (www.tummyteam.com) and the results were amazing! I saw one woman lose four inches in four weeks! Anyway, it's a super simple exercise, but if you need help getting motivated, I recommend seeing Kelly. She's in Camas, which I think is close to you... You can always email her for advice and she sells Julie Tupler's books and DVDs, but I found them to be a bit confusing on my own - a bit wordy. However, you'll never do another crunch again and you can do the exercises in your car! The workshop was over a six-week period. We met for three evenings and each time were shown more exercises and so we worked up to doing them all.
As for diet, if you're interested, I'm doing the 17-Day Diet by Dr. Mike Moreno. The first 17 days are pretty intense, because you don't eat any carbs at all, except fruit and veg, but it really works to help you drop weight fast and I figure I can do anything for just 17 days! I did nutrisystem and lost 25 lbs, but then got bored after I plateaued for a while and couldn't stand the food anymore. This one is better for me so far...
Anyway, good luck!