Ant Control on Simple Pest Control has a huge list of ant control techniques (even mentioning your boiling water idea, which I'd never heard of - I'll have to try that!). It includes a lot about behavior control, ie, keep them from wanting in your house to begin with, to keeping them out of the areas you don't want them in, etc.
The Biological Control section lists several natural ways of getting rid of ants:
Make your own boric acid bait to kill ant colonies. Ant baits are the cornerstone of all ant control. Instead of spraying poisons everywhere, which can split colonies up and potentially make ant control more difficult, you bring the ant to the poison. The worker/foraging ants then take the poison back to the nest to share with larvae and queen. This is how colonies die, or are reduced to acceptable levels. Boric acid is a perfect ant poison. It’s cheap, natural, and much less dangerous (though not harmless) than commercial poisons. Best of all, when mixed correctly, boric acid is a slow ant killer – it allows ants time to bring it back to the nest in sufficient quantities for an ant apocalypse. Here are a few boric acid ant bait recipes:
Mix three cups of water with one cup sugar and four teaspoons of boric acid (Borax). Pour around a cup of solution into separate jars. Pack the jars with cotton balls to about the halfway point. Seal the lid and poke a few holes at the center. Make a fun skull-and crossbones label and set the jars out in ant trails and hotspots.
Some ants prefer protein and grease over sugar (little black ants, thief ants, pavement ants, big headed ants…). Replace the sugar in the above recipe with canned pet food. Or try this recipe: Mix four tablespoons of peanut butter with six tablespoons of honey and one teaspoon Borax.
Use diatomaceous earth – the slow ant killer. Most ant species are susceptible to diatomaceous earth, a desiccant dust consisting of the fossilized shells of ancient algae. These shells are covered in microscopic shards which create cuts in the cuticle of crawling insects. The ants walk over the DE, start leaking, dehydrate, and die. You can apply DE as an ant barrier around the outside of your home or inside, around the perimeter of rooms and carpets (be sure it’s food grade). You can mix DE in water to make a paste to apply to trees. You can get proactive and dust nearby anthills. Using a duster, you can apply DE to the cracks, crevices, and wall voids, where it will remain effective forever.
Capsaicin – a natural ant repellent. Chili pepper, black pepper, red pepper, ginger, and paprika all contain capsaicin and so can be used to repel ants. I’ve heard of people using it as a barrier around homes, but it is best used in gardens. You can apply these powders around the base of plants or in wide bands (5-6 inches) between rows.
Citrus oils kill ants. Linalool and d-limonene - citrus peel extracts found in products like Orange Guard, Citra-Solve, Bugs’R’Done and Pro-Citra DL Aerosol – can be used for ant control in a variety of ways. They can be used as a direct kill spray, a repellent in gardens, as a drench for anthills and outdoor nests, or for treatment of cracks and crevices where ants are nesting indoors (may stain).