i do a mix of yoga and pilates and get great results. i do yoga for abs in the morning, pilates in the afternoon, and yoga for resting at night. Are you remembering to pull in your core while you do these positions? Alot of times that's the number one mistake. Kim Kardashian wears a corset to help her remember. Perhaps this would help you too.

a few friends of mine who recently lost weight and really thinned out in their midsection said pilates and running were there main ways to target abs.

a really great core strenghtening exercise is to do the plank.

1.Lie face down on mat resting on the forearms, palms flat on the floor.
2.Push off the floor, raising up onto toes and resting on the elbows.
3.Keep your back flat, in a straight line from head to heels.
4.Tilt your pelvis and contract your abdominals to prevent your rear end from sticking up in the air or sagging in the middle.
5.Hold for 20 to 60 seconds, lower and repeat for 3-5 reps.

if you find that a little difficult, try doing it with your knees on the ground and your feet up in the air. even just diong that a few days a week really helps

doing crunches, hovers ect will only strengthen the abs, not let you spot reduce weight in that area. My guess is that you will need to loose weight until it comes off your stomach (where you loose your weight from first is different for everyone) and only that will really flatten it
the best thing to do this is any high intensity cardio.... running, cycling, aerobics but your going to need to get the heart rate up to burn any significant calories

You can do all the spot-specific exercises you want, but it will only work so much. Cardio is the big fat reducer here. You need to work the whole body, notice runners, dancers, swimmers...all are pretty much lean bodied. Pilates and Yoga are great as well, but maybe take some fun cardio classes like Step, Kickboxing, Zumba, etc. Good luck!