I use a sugar based product called Terro, and it is very effective. I am not sure if it’s organic. We just put a dime-sized dollop on several pieces of cardboard near our baseboards and it works every time.
In the event that it’s not organic, you might try diatomaceous earth, which is. However, I haven’t read about its efficacy on ants.
You can always consult an entymologist with your state’s cooperative extension service. Here’s a link to the University of Minnesota’s extension brochure on ant control: http://www.extension.umn.edu/distribution/housingandclothing/dk1015.html