I'm working on a big sugar-y baking story for an upcoming issue (get ready!) that happens to call for a lot of chopped chocolate—pounds of chocolate. If you've ever chopped that much chocolate you know how important it is to use the right tool.
For large chunks, say 1/2-inch or more, the tip of a sharp chef's knife is great, but it puts holes in your butcher block. I much prefer using a chocolate chipper. The wood handle is easy to grip and the tines break the chocolate into pretty uniform chunks—great for chocolate chunk cookies.
If I have to finely chop the chocolate, rather than use a chef's knife, I've found that serrated knives or scalloped-edged slicing knives work the best. This one from Wusthof called the Super Slicer efficiently shaves the chocolate so finely that one pass is all you need.