Protein and fiber are your best bets if you want to fill up. This is hard for me, personally, because I'm not a big meat eater (or veggies!) and am a total carb addict. However, when I just can't fill that hunger, eggs seem to work well for me. 2 eggs (fried with PAM, not butter - or hard boiled if you prefer) are only 140 calories and fill me up for hours. A spoonful of peanut butter is a good snack, too...and takes a while to eat if you just lick it off the spoon. Carnation Instant Breakfast is another fave of mine, with skim milk.

Also, keep in mind that it takes time for your brain to adjust to less food if you're used to eating a lot during the day. Sometimes, a glass of water, drunk quickly, will temporarily fill me up enough to let me wait another hour or two till my next meal/snack. Or chew sugar free gum if you just need to gnaw on something. Or distract yourself...go for a walk, do housework, etc.

In the end though, if you are truly hungry....eat! Denying yourself constantly is diet sabotage and will just stress you out and result in a gorge-fest.