DD2 is 2 1/2, and she became a pest for waking in the night and asking for a cup of milk. I bit the bullet one day and decided, that even though I knew just by giving her some, she would go back to sleep, it was becoming a habit. So.
She was fine for a couple of nights. I said I would get it for her, but didn't and she just went back to sleep. Then one night (at about 3.30) she decided to kick up a stink about it. She got up and down, and I kept putting her back. She cried and tantrumed, and I kept putting her back. She kept this up for an INSANE quantity of time, and eventually at 5.30, she stayed in her bed, and went back to sleep. I got up, as I was due up at 6 anyway. It was a loooong day.
But you know what? She hasn't done it since. No - I tell a lie, she has VERY occasional waking, normally with something I can forgive, like a nightmare, but she chances her arm, and asks for milk, and I tell her we have none until the milkman comes in the morning, and she accepts this and goes back to sleep.
Oh - and I also threaten that the door is shut if she keeps getting up. And I stick to it. Good girls who are in bed, get the door left ajar. Works at nighttime too.
Gawd bless Tanya Byron!