For definition do these, each exercise for 1 minute and then immediately followed by the next exercise:
Trunk Twists
Standard Crunches
Alternate Bicycle
Oblique Crunches
30/Side)
Leg Raises
As you get good and able to do it straight for 5 minutes all exercises, you can add some weights, dumbbells and belts on your legs and arms. Don't over look trunk twists, they are important for warm up and obliques.
This workout alone combined with small meal diet produces definition other people can dream of. Such as you stand next to a guy who does machines for an hour, and you have more defnition. It's harder than machines as well.
Keeping up with this set means cardio heart rate pace, so you're burning fat too.