Well I am sort of in the same boat, with the stomach. Some people would be okay with my stomach, but I'm a very self concious person, so that doesn't work so well in certain cosplays.
But I suggest the following:
Any sort of stomach exercises:
-Using a heavy object, sit on your glutes with your feet slightly in the air and shift the object from side to side, over your torso.
-Med Ball Crunches
-Using a Swiss Ball and a Med Ball, sit on the edge of the Swiss with your feet firmly planted on the ground. And hold the Med over your head and lean back until you feel your muscles flexing thensit back up into a comfy position.
-this can be done with practically object: I sujest a bar with resistence or dumbell's.
Mixes of Both:
- These are when you lay on the ground then lift your self up on the lower part of your arm and toes. The objective is to make your back as straight as possible. To add the difficulty and work of your core, do this on a Swiss ball and roll out onto the floor as far as possible with your legs remaining on the Swiss. (You may want to look this up.)
You can find more here:
I hope this helped a little. You may want to google a few of them by name.
Cosplay List 2010-2011
Miku Hatsune-Vocaloids 90%
Shirley Fenette-Code Geass 100%
Orihime Inoue-Bleach 100%
America (Alfred Jones) -Hetalia Axis Powers 95%