I would definitely say oatmeal. You can make it with milk or water and have a glass of milk with it if it helps fill you up. And berries is great in it.. apples is my favorite. Apples and cinnamon together is like eating apple pie oatmeal

I also like cut up melon or orange slices alongside it sometimes.
I make a "mock" mcmuffin sandwich sometimes that even my kids love. I take a small mug or lil glass dish and whip up 2 egg whites and then microwave it for a couple minutes. I put this on a low-cal english muffin or toast with a slice of tomato or a slice of fat free cheese melted on top or maybe a small piece of canadian bacon or ham. It's very filling and versatile.
You can make your own breakfast burritos. Scramble an egg with lots of veggies and spices and roll up in a pita or small tortilla. Also very versatile.
If you dont want to cook/microwave - If you like cottage cheese (many people dont) - I like having this with fruit immensely. I also like yogurt with crumbled granola/cereal or fruit. Sliced up apple w/ yogurt dip. Piece of string cheese and fruit or nuts.
Also remember - just cause its breakfast doesnt mean you cant have other things.. like a salad or a english muffin pizza or a sandwich.
