Terro is the most effective ant solution we've ever used. (Granted, we've never hired an exterminator, but we've never had to go that far, either). When you use Terro, you only put small drops of poison in the busiest ant traffic areas (preferably as close to their entrance to your home as possible). They eat it and take it back to the colony, and it wipes them out.
We've got kids and pets, so we don't like the idea of a more intrusive pest control. Usually, our problem is resolved quickly (except for last year when we had difficulty finding the source of the invasion).
Also, treating your yard for pests can help eliminate problems in the house. The years we've done that, we've seen a huge decrease in everything from spiders to ants. (Incidentally, we never got around to it last year, which was one of our worst bug years in awhile!)
Good luck!