OK, I lay on the floor and do crunch after crunch. What are at least 3 different and effective abdominal flatteners?

A resist-a-ball will be your best possible investment. Sit on the ball and put your knees against a wall, do 4 sets of 25 and try to keep a contraction. Do side to side sit ups as well. Of course your best best is to sign up at a gym and use the abdominal machines with resistance. Results should be noticed in 3 to 6 weeks.

In pilates class, we do an exercise where you raise your torso and legs so you make a V. That seems to work a lot of the Ab muscles.

The first thing to consider would actually not be the muscles themselves but what covers them. Yes, I am talking about fat (I know, gross). If you have a problem there, which I am guessing you don't (if you don't have a problem there than skip this paragraph entirely), concentrate on workouts to burn fat. (May I suggest turning up your favorite fastpace music very loudly and rockin' out or whatever that gets you out of breath for about half an hour each day) Eating propperly would also be of importance. Now I am not saying to cut your food intake in half and stop enjoying sweets. Only start looking for foods with fats that your body can use for energy,aka unsaturated fats. Try to avoid transfats and saturated fats.
Now if you don't have a problem with flub, you should concentrate on excercises that lengthen and tone your stomach. Usually crunches are not the answer because after about twenty your body starts to fatigue (or at least mine does) and then use loose your correct posture. But if you are going to do them concentrate on keeping your abs constantly engagaed to keep your movements smooth and rhythmic. The key to any abs workout is to keep your abs as flat as you can and don't allow it to pudge up when you contract. Pilates does a very good job of encouraging this and really does help achieve flat abs.