We will limit the top 10 cereals to the US, as going abroad would be more difficult. In all likliehood I would hazard rice as the top one for the world.

So according A.C. Nielsen Financial Services. The top cereals are:

Name

1. General Mills Cheerios
2. Kellogg's Special K
3. Post Honey Bunches of Oats
4. Kellogg's Frosted Flakes
5. Kellogg's Frosted Mini Wheats
6. Kellogg's Raisin Bran
7. Kellogg's Froot Loops
8. General Mills Cinnamon Toast Crunch
9. General Mills Lucky Charms
10. Quaker Oats Cap'n Crunch
11. Quaker Oats Life
12. Kellogg's Rice Krispies
13. Kellogg's Corn Flakes
14. All Others Combined

Yes I know this is more than 10, but it is interesting from the reports I have read that Kellogg's takes 5 of the top 10 and in 1995 they had 12 of the top 15.  These stats are based on dollar sales (total units sold times average equivalent unit price).  For the the year 2008 each percentage represents $62 million dollars.  Also each item is total percentage for it's lineup - in other words if there are special flavors or issues put out they are included.  IE All flavors of Honey Bunches of Oats are combined. 

• 1995 Source: Advertising Age (09/30/96, p. S14) from Information Resources as published in Market Share Reporter - 1998.
• 1998 Source: Advertising Age from Information Resources (supermarkets only) for the 52-weeks ended Dec. 27, 1998, as published on the AdAge website
• .2005 Source: A.C. Nielsen Financial Services for the 52-weeks ended July 16, 2005.
• 2008 Source: A.C. Nielsen Financial Services for the 52-weeks ended June 8, 2008.

The top three manufactures of breakfast cereals are in order:

1. Kellogg's
2. General Mills
3. Post

Of the top cereals how do they rank in terms of nutrition based on " A Calorie Counter" ranking according to ingredients.

Only one of the top 13 was in the good for you nutrition:

• General Mills Cheerios

How about worse for you:

• General Mills Lucky Charms
• Kellogg's Frosted Flakes
• Kellogg's Fruit Loops

The rest fell in the middle of the pack.

Now if you are concerned about Trans Fat, there is only one of the top listed that has this no no in it:

• Kellogg's Froot Loops

Note: on the Trans Fat, it may not be listed on the nutrition label but according to the FDA if there is less then .5 grams per serving they don't have to list it.  So pay attention to the ingredients when you see the term "hydrogenated" or "partially hydrogenated," that means there is indeed trans fat present in that food.

Cereals having 100% the needed supplements such as vitamins may sound like a first choice. But for the manufacture it only cost a few cents to add those vitamins, and they charge you a premium ( 40 cents or more than similar brands). If you are around 25%, remember the milk and rest of breakfast could supplement that. Plus no cereal will meet your calcium needs so add milk.

A suggested nutrition guideline in picking cereals based on their ingreadients and nutrition labels:

• 100-200 calories
• At least 2 grams (preferably 3 or more) protein
• At least 3 grams fiber
• No more than 8 grams sugar
• No more than 3 grams fat
• Approximately 25% of the Daily Value for key nutrients (iron, folate, B6 and B12).

Additional thoughts on extra ingredients:

• Cereals with nuts will have more fat.
• Cereals with fruit will have more sugar.
• Nutritious cereals - straight out of the box - make great snacks.
• Also extras like soy protein, flax, other fruits may be too small to really matter in your overall health.
• If it has sugar listed as the first ingredient - ditch it now.
• Whole grains are preferable

Finally remember Breakfast is your most important meal of the day.  Fact is starting off with it as your largest meal, and working down to smaller meals during the course of the day can make a difference in weight loss.  Same calories flipped around, loaded during the early day is better for you.