currently studying my gym course: the following will give you a ripped stomach and abs.
Sit ups
Abdominal curls (1/3rd sit up)
Abdominal twists
Back extensions
Prone fly's
Burpee's
I would also suggest 5kg star jumps (5kg dumbbell in each hand)
Chin ups will work incredibly well.
For best results do reps of 20 and then move on, try to complete 3 sets of these in one go.
Good Luck