Sprinkle Sevin Dust on the mound and then a bit of water.
Poke a hole in the mound and pour boiling water inside.
This method has worked well for us.
Get a box of Jiffy corn mix, open it and sprinkle it around your garden or where ever they are. The worker ants take it back to the colony and it kills them. All but the queen, who is responsible for reproduction. Repeat if necessary. You will need poison to destroy the queen.
Another great product is Terro, a liquid found in the pest control sections of diy stores. Follow the package directions. We use this mainly on deck where you can see parades of them. Expect to see an incresase at first because they are coming out to feed.