This is the feeling I get everytime i gotz the munchies.
Drink A LOT of water with your meal, it will make you feel full long enough for the cravings to pass.
This helps, but the difference between hunger and appetite affects everyone in a different way. I know the EXACT feeling you were talking about, my stomach is full and I've eaten a huge meal, but I'm still hungry. I forget the name of it, but there is a hormone that makes you feel "hunger" regardless of anything you eat/have eaten. I remember seeing them showing the effects on mice on a news show once.
The only way I can get over this is to log what I eat, so I know how many calories/protein/fat/carbohydrates I've eaten, and just ignore the feeling of hunger, and look at food like fuel. It's really tough, and it sucks that genetics can make you hungry for no reason, but I look at as another chance to strengthen my self-discipline.
Anyway, something else it might be is if you have a deficiency in something, which may make you still hungry or craving for something. Make sure you have a good multivitamin, ever since I started taking Optimen, I don't get random food cravings anymore. Just hungry all the time lol