For the glorious six-pack!
Lie on your back, place your hands behind your head, elbows out to the side. Bend both knees at 90 degrees, feet off the floor. Squeeze your abs tight and lift your shoulder blades off the floor while simultaneously lifting the hip off the floor. Shoulders and knees should come in towards each other.
Do 16 reps, rest and repeat twice over.
Also see: Making 'quality time' count!