A cereal that has a good balance of fiber and protein and low in sugar (I like Special K Protein Plus)
Whole wheat toast
Any combo of the above (depending on your calorie ranges) can be quick, easy, and fairly inexpensive. If I'm having cereal I'll have some (not from concentrate, 100%) fruit juice. If I'm having cottage cheese I'll have some whole wheat toast and juice, etc. I like to get a good balance of carbs, fiber, and protein in at the beginning of the day. The above items are staples in my kitchen so breakfast ends up being one of my easiest meals for the day.