EVERYTHING with milk/milk products in it. DS2 is also such a happy boy which is why I was convinced there was something wrong, I just couldn't work out how he could be so happy yet such a terrible sleeper (as in wake up clearly uncomfortable, only sleeping upright etc). So I don't eat:

Milk (I now drink rice milk)
Cheese
Yogurt
Ice cream
Particular condiments with milk solids (some mayonnaises, Caesar dressing etc)
Biscuits
Chips
Butter/margarine (I use Nuttelex)

Basically I read the ingredients list of anything I eat, you'd be surprised what dairy is hiding in. Even the breadcrumbs I went to use had milk solids!

If you're willing to give it a go then might be worth a shot. I do take a calcium supplement just to ensure I'm getting enough calcium