I would think that brisk walking (a.k.a. power walking) is great for slimming down thighs, butt, and stomach, especially for beginners. If you're wanting something more rigorous, then jogging would work just as well, though it's harder on the joints. If you have joint problems (like I do), then I would stick to brisk walking, bicycling, and swimming. Those count for cardio workouts. It would be more effective if you teamed up those exercises with strength exericises that target those specific muscle groups, like ab crunches, lunges, and flutter-kicks. Good luck!!
You can't pick and choose where fat leaves your body.
Welcome TGM!
The short answer you're looking for is:
Any excercise that you enjoy doing on a consistent basis that well help you lose more calories.
But that is a very small piece of the equation
If you want fast, consistent fat loss its going to require a little work and learning but this is a great place for that!
and yes, unfortunately Steve is correct. You cannot pick and choose where you lose the fat
yes Steve, many of my friends told me the same but I just dont want to believe it and hoping for miracle ( that there is a way to slim down where I want )

Unfortunatly (and I hate to hear this too) there is no one specific exercise that will target your legs or belly.
Remember, muscle burns calories all day!
<quoted>Remember, muscle burns calories all day!
As does fat, organs and connective tissue.
When inactive though, muscle doesn't burn all that much more than fat from what I've seen. Based on the amount of muscle I've added over the years onto my frame, anecdotally I'd agree too.
Well what do ya know! I've always had this image of muscle sitting there burning away all my calories while I sit at a desk. Like "build up enough muscle and then you don't have to do anything for a week while it does it all for you!"
You mean I actually have to keep eating right and working out?! Bummer!