What's the best exercise to work out your stomach? And what about your thighs and hips?

You can do a lot, your average sit ups and push ups given you put in the effort to go the extra mile can help a lot. Just do 30 a day and try and increase the amount monthly. Also there is this Youtube channel which is a great way to work out at home for free and again given you put in the effort you will get stronger.

http://www.youtube.com/watch?v=vkKCVCZe474&annotation_id=annotation_23822 5&feature=iv

Belly fat tends to respond best to a low carb diet (cut out all the sugar, bread, rice, pasta, potatoes etc) and eat more protein and green veg. Fat on the hips and thighs but not the waist tends to need a low calorie diet.

You can't spot reduce. That means you can do sit-ups all day long, and you'll have very strong stomach muscles which are still covered by a layer of fat. You have to get the diet right, and do cardio to burn fat. Cardio is any exercise which makes you puff and sweat for at least 20 minutes, and strength training, which makes your muscles more shapely.

If you don't have access to a gym, do squats, press-ups, pull-ups, lunges, step-ups, plank, woodchopper etc.

Are there any diet pills that would actually work to help lose weight? Also is there any exercises to get rid of celulite?

There are no over-the-counter diet pills that do any more than a cup of coffee would (most of them are based on caffeine) and you need a doctor's prescription for the others.

If you want to take something, take a fish oil supplement (lack of essential fatty acids slows fat loss), some vitamin C (low levels of vitamin C make fat loss harder) and have some sugar-free jelly for dessert (the protein in gelatin has a very high satiety level, so you'll be less likely to snack). Avoid sugar. The body will not burn fat while there is a high level of insulin present.

There are no specific exercises for cellulite, but regular frequent massage can help.