I know two people who are having huge problems with carpenter ants, and I myself have gotten an infestation of small ants in my garden, although I don't know that they will hurt anything. Here are some things I've read about that ants supposedly hate:
vinegar, cayenne pepper, citric extracts, bone meal, cinnamon, cream of tartar, salt, and perfume, powdered charcoal, tansy, pennyroyal and southernwood.
You can try adding cayenne pepper to the boiling water, or using citrus extracts.
If you have multiple nests, you could dig up a bucket of ants from one nest and dump it on another nest. Ants are very territorial, and they will readily hunt and kill invading colonies
"Dehydrate them by laying out piles of instant grits ( a corn product usually located in the cereal section of the grocery store) at the point of entry and along their trail. They will think of the grits as a food source and consume the pellets. The grits will in turn absorb moisture from the ant's body, thus killing it (instant grits are specially formulated to absorb water more rapidly than regular grits, thus they are more effective)"
Regarding that last one, the myth is that the ant will explode, but I do know that diatomacious (sp?) earth will dry them out. Ultimately, if you can eliminate the queen somehow, the whole colony will die! MMmmuuuuhhhhhaaaaaaaahahhahahha!!!!