Fipronil is a slow-acting ant poison that hasn't shown any toxicity in dogs and cats. Long range studies of its effects on human beings suggest that it's probably harmless, and it's used in several products, such as PetArmor and Frontline, that protect cats and dogs from ants. These products are widely available at pet stores and on the Internet.
Be careful before you use fipronil with pets other than cats and dogs, though. It can be fatal to rabbits, as well as to certain kinds of birds and reptiles. Although fipronil could turn out to be the ideal solution for your pet's ant problem, you should do research first on the product's effect on other types of animal -- especially if you have a bunny that likes to snuggle up with your kitten or puppy. Ants are a problem, but you don't want the solution to turn into an even bigger problem.