1) The Sun Valley Ski Tool (SVST) aluminum Pro Edge Beveler ($40 with clamp) is an angled piece of metal to which you clamp your files. The 92-degree bevel is all most nonracers need.
2) This SVST World Cup Sidewall Plane ($155 with carbide bit) lets you remove a thin layer of sidewall material above the edge so your files and stones can make contact with metal. A pricey tool—that lasts.
3) A true bar, like the FK 120-mm ($13) from Reliable Racing, is essential. Hold the knife-edge against the base and then sight down the ski—there should be no light beneath the center of the bar, and the edges should slope slightly away from the base (that's your base edge bevel).
4) These SVST Superchrome Lazer Kut Files ($15—$16) are sharper and more durable than anything at your local hardware store. Clamp the six-inch file into your edge beveler; use the eight-inch for your base edge with either a beveling sleeve (SVST has plenty of options), or a business card or two under one edge to provide a bevel. (Tip: Never backstroke a file—you'll knock the teeth over.)