Another vote for oatmeal! I do steel cut oats, with cinnamon and vanilla, with a berry blend on top. I'm going to have to get some of that Sam's mix, right now I get my from Schwan's.
My other favorite cereals are the Strawberry Yogurt Burst Cheerios and Quaker Crunchy Corn Bran Squares. Neither of them is really a hearty breakfast, but I like them anyway. Yogurt Burst I only eat on the weekend, when I'm not running and don't need something to stick to my ribs. Corn Bran I eat with yogurt as a snack. Crunchy, very slightly sweet, and quite fiber-y.