Here's a good exercise for those obliques that I use with athletic clients who are looking to get that little extra.
Attach a single hand grip to the low pulley on a cable machine.
Lay flat on your back and put your left foot through the single hand grip.
using the pin load on a low weight, now bring your knee toward your chest, like a row movement. lower and repeat, not allowing your foot to touch the floor. 10-15 reps, then change foot and repeat with your right foot.
This is challenging, and will target your Apollo's Belt beautifully.
But I must agree with all of the above, obliques and abdominals in general have a lot to do with genetics and body fat %. Cardio is excellent for reducing body fat, along with good diet. But for some of us, that ripped 8 pack may simply never appear. Regardless, it is good to work on this area strongly for good all over health and fitness.