This website has a lot of workouts laid out so that if you want an idea of what to do, you can grab one and go. The filter at the bottom of the page lets you select the type of workout (abs, strength, HIIT, etc) if you'd like to filter it down.
Hurts like hell --> No Pain No Gain Fat Burning Ab Exercises. Burn fat and slim down while toning up your abs and strengthening your core. Repeat the circuit once or twice more. Click the image to see the moves in GIF form.