Getting lean enough to expose your abs is a function of proper diet and proper programming of exercise fundamentals.
It is not a function of all sorts of abdominal training like some above think.
We all have abs. Those of us who can't see them are carrying to much body fat. We need to lose the body fat in order to see the abs. Not build the abs to see them through the fat. It's that simple.
So how do you reduce body fat?
First place to focus is your diet. Primarily, you want to make sure you are expending more energy than you are taking in each day. Eat less than you burn. Most people translate this into hours of cardio each day to create that burning more than you are eating scenario. This isn't correct. There is a cost to anything you choose to do. The idea is to make this cost work for you, and hours on top of hours of steady state cardio is not the solution.
Instead, figure out how many calories you need to maintain your current bodyweight. This can be done using multiple methods. For starters, you could simply assume that 14-16 calories per pound equals your maintenance. Or, you could track your food for a week or two. If your weight is staying constant during that 2 week period, it is safe to assume you are eating around maintenance and you can start from there.
Once you figure out your maintenance, you simply reduce your intake below this level to assure yourself that you are burning more calories than you are eating.
What you eat, of course, is important too. I'd shoot for approximately 1 gram of protein per pound of lean body mass. If you aren't too fat, you could use 1 gram o protein per pound of total body weight. With fats, you could shoot for .25-.5 grams per pound of body weight. This should be comprised primarily of the good stuff (read: fish, fish oil, nuts, olive oil, flax, etc.) There will of course be some amount of saturated fat in the diet from the meat that you eat. That should be the extent of it though. The remainder of your food can come from carbs or even more fats.
Track your weight, body fat % maybe, and certainly measurements of various body parts. If things are not heading in the planned direction, it's time to modify your approach.
You see, there is no such thing as a "routine" or "program." Most people don't understand this concept and they spend their time (years) searching for The Way To Train and it just doesn't exist.
It would serve you soooo much better understanding the basic fundamentals of training and learn to apply them to yourself through trial and error.
The big picture is this: Create that energy deficit I spoke of originally. Without this, you aren't going to lose fat. After you get this programmed as habit, you can start toying around with "setting" the macronutrient profile of your diet.
In terms of exercise, anything is better than nothing. Just being more active in general will aid in this negative energy balance. The more active you are, the more food you can eat. The idea is to be as active as possible while allowing for enough recovery so that positive adaptations can occur. Over-tax the body systemically with too much "work" (especially while dieting) and progress will stall.
So again, it's about finding balance between working enough yet not working too much.
This is why it's a little tricky. A properly executed program will include resistance training and cardio. Most people overemphasize the cardio side of things when this is the least effective tool in the bag. And the people who actually do utilize resistance training usually do it retardedly. There is plenty of stuff written up about this in the stickies. I suggest doing some research on "how to resistance train."
It would serve you well to read the "words of wisdom" stickie created by TomO.