Just a couple of exercises, applied correctly, can quickly raise the tension applied in the four abdominal muscle groups making for that strong-abs feel you're looking for. 2-Move Abs is a workout that offers you exactly that. Zero space requirements, you can literally do it in your underwear (make sure, beforehand, you're at home) and it will change the way your abs feel and look. More importantly, it will change the way you use your body.
Extra Credit: 1 minute rest between sets.