There are some chemicals you can use to spray the perimiter of your house, but personally, I would just let them be. And not just because of my buddhist mentality. Make sure you aren't leaving food or sugary substances outside that will attract them. We've been having a terrible time with the teeny little ants but the problem is inside. We've put out traps and sprayed and the whole gammat. But we've found that if we just really keep a tight lid on crumbs and spills and whatnot, the problem corrects itself.
If you are seeing big carpenter ants, you might want to call an exterminator as they can do significant damage to your home.
EDIT: Found this information on this website - cool!
http://eartheasy.com/live_natpest_control.htm
The first line of defense is to remove the attractants: keep counters free of crumbs and sticky spots. Cover the sugar and put the honey jar in a plastic baggie. Cut off water sources such as drips or dishes left soaking overnight.
If the ant invaders persist, try these simple measures:
Keep a small spray bottle handy, and spray the ants with a bit of soapy water.
Set out cucumber peels or slices in the kitchen or at the ants' point of entry. Many ants have a natural aversion to cucumber. Bitter cucumbers work best.
Leave a few tea bags of mint tea near areas where the ants seem most active. Dry, crushed mint leaves or cloves also work as ant deterrents.
Trace the ant column back to their point of entry. Set any of the following items at the entry area in a small line, which ants will not cross: cayenne pepper, citrus oil (can be soaked into a piece of string), lemon juice, cinnamon or coffee grounds.
Mix a half teaspoon each of honey, borox, and aspartame (Equal, Nutrasweet, etc.), in small bottles. Place bottles on their sides, with lids off, in areas of most ant activity. Ants will carry the bait back to their colonies. Important: use indoors only; must be kept away from pets and children.
Leave a small, low wattage night light on for a few nights in the area of most ant activity. The change in light can disrupt and discourage their foraging patterns.
Ants on the deck? Slip a few cut up cloves of garlic between the cracks.