There's a whole lot you can do for your abs. I don't know if you have access to a gym, but there's a lot you can do at home. You shouldn't cut short the benefit of conventional exercises, such as crunches, leg raises, pushups and pullups. I don't know what kind of physique you have, or what kind of diet you follow, but generally for tone, you should do your exercises in circuits. These keep the pressure on the part of the body you're working out. Go from one exercise to another in quick succession. Do about 4 exercises. An example for your abs, is 20 crunches, followed by 20 inverted situps, followed by 20 (3 count) scissor kicks, followed by a 20 second 6" leg raise. Break, and repeat, break and repeat. Modify the exercises to what works best for you, but make sure they all work the same section. As you progress, increase the reps per exercise and shorten your breaks.
I'm hardly a nutritionist, but put simply, try not to intake more calories than you intend to burn in a day and between meals. Aside from following your own workout plan, eat three meals a day of moderate proportion, the largest being breakfast. If you have a small breakfast, compensate with a slightly larger lunch. Keep your metabolism awake and processing beneficial foods. Suger = Satan. There are plenty of sites out there that offer diet plans, or suggestions on balanced meals.
There are a lot of machines that can dedicate themselves to the midsection at the gym, some you wouldn't think. The key is to somehow throw yourself a little off balance. Doing that will force your midsection to compensate.
One example of a workout not typicaly associated with abs that can be is pullups. Hold the bar with one hand in the chinup position and the other in the pullup position, and do as many as you can. If you can't do one, jump and pull yourself up with momentum, and very slowly let yourself down. Try to do that repeatedly, with short breaks inbetween, until you can do it slower and slower, and finally until you can do full pull ups.
Pullups work your entire upper body, and this way most of your midsection as well. Pushups, also are very effective at toning your upper body and midsection.