Raid Ant and Roach Spray did the job for me when ants invaded my garage this summer. You will use the can up rather quickly but it does work great. Try not to overspray since a little will do the trick.
Spray directly on the pests if possible and around the area they appear to be coming in. Repeat this process the next day or if the area gets wet. In my situation the ants were gone the next day and have not reappeared since. It kills on contact and seems to keep the ants from wandering into the sprayed area.