One thing that worked out AWESOME for me and that may be a little counter-intuitive is popcorn. Not bagged or theater, but made at home in a hotplate style popper. Something like: http://www.amazon.com/West-Bend-6-Quart-Electric-Popcorn/dp/B00004RC6R .
Popcorn’s surprisingly low calorie when you don’t overload it with butter and oil. A popper like this allows you to control the amount of oil you use, and without anything else added on, you’re essentially eating popped grain. I’ve used a 3-quart serving of butterless, lightly oiled, seasoned (pepper, garlic, cayenne, oregano, etc) popcorn as dinner replacement before (but then, I tend toward big lunches). Alternately, stale popcorn makes for a great snack.
Plus, it’s super friggen cheap.