For general unspecific hunger a large cup of peppermint tea or liqorice tea often works for me. Or a large glass of water with a few drops of peppermint essence in.
Another trick is, if you are craving something specific, to try and analyze what exactly is the taste you want, and then find something low cal that has the same taste. For me it is often salt or grill taste i want when I'm craving fries or burgers. Then I pour a small amount of barbeque seasoning on a small plate and "snack" on it by dipping my finger in it and licking it off. I know it sounds strange, but it works well for me. I get the taste I want without the calories.
Some people think that specific cravings are a symptom that you are lacking some vitamin or mineral in your diet, and so a daily multi vitamin pill would prevent these cravings.