In the summer you want the ceiling fan to spin in a counter clockwise direction so that air flow is pushed down. This will create a windchill affect and cool you down. It can make a room feel up to 8 degrees cooler and help you save up to 40% on air conditioning costs.
A fan spinning in a clockwise direction will be best during the winter, as this creates an up draft and helps to recirculate heat down. This can help you save money on heating costs (up to 15%).