I am generally the last person to recommend eating cereals, mostly because the ones that a marketed as healthy are still laced with sugar and they have little nutritional benefit. All you need to do is look at the first post in this thread to realise that there is something really wrong in how cereals are marketed.
Corn flakes it pretty much empty carbs and yet there is this perception out there that it is healthy and don't get me started on nutri-grains. Nutri my arse.
Further most people do not stick to the serving size recommended on the box, hell weet-bix even encourage you to eat more than the recommended serving size and on its own weet bix is not a well balanced breakfast and a lot of people add sugar to it.
Anyway I have come across an excellent cereal range, high in fibre and protein and not to high in sugar.
http://goodnesssuperfoods.com.au/
The Protein first cereal is the one I choose, it only has 7.7 grams of sugar per serve and 13.2 grams of dietary fibre and 8.7 grams of protein. Yes they're relatively expensive, but they are much better option than any commercial cereal I have come across.
If you are going have cereal have a serving of fruit on the side to make it more well balanced.
As has already been stated in this thread, oats are probably your best bet, they're cheap, they're healthy and they're pretty convenient. Just make sure to avoid the flavoured Quick Sachets, they are generally loaded with sugar. Try dicing an apple and adding it to hot porridge, it actually tastes pretty good.