Valrhona still makes the best overall range of dark chocolates in the world, but there are a few individual chocolates from other manufacturers that are also in that league. Chocovic’s “Ocumare” is an outstanding example of Venezuelan Criollo cacao. Divine Chocolate is a fair trade chocolate well-crafted from Ghanan beans (some of the best Forastero cacao in the world). Chocolaterie de l’Opera in France makes superb chocolate, but good luck getting it in the States. Ditto for Cluizel, another French firm. There are no American chocolate makers yet that approach this quality level, but Guittard is trying hard, and may yet succeed. Some foodies like Scharffen Berger, but I find it way too acid (not enough conche time).
For milk chocolate, it’s hard to beat the Belgians. Callebaut makes several very good ones.