Your body digests protein slowly, which is why it helps you feel full after eating. Check out this chart to see how much protein you should be eating each day, then you can figure out how much you need for each meal and snack.
Marci recommended getting at least 30 grams of protein at your main meals to keep hunger at bay between meals. Eggs or egg whites, nuts, beans, tofu, chicken, salmon, and protein powder are excellent sources.