The Athame is one of the most important Magickal tools. It is traditionally a black-handled, double-edged knife. It need not be sharp, as it is used for directing energy and not cutting. Once consecrated as your athame, the blade should never be used for cutting anything. A white handled knife called a Boline is for cutting inside the circle. The athame may be used to carve symbols into candles but for little else that involves cutting of any sort.
The athame may be any color, shape, and size. Use what you feel right with. The athame is normally associated with The God and the element of Fire. Here are a few links to places where you can buy athames online: