Valrhona is probably the highest regarded brand of quality chocolate, especially in Europe. It's used a lot by dessert chefs in fancy restaurants. Lindt is another great brand, and easier to find than many of the others.
If you want to try something different, try chocolates made in Modica, Sicily. They use a special recipe without milk that gives the chocolates a unique, grainy texture and a subtle taste. From personal experience, CioMod is a good brand.
When it comes to pralines, my favourite brand is Daskalides. But some of the best can be found in small shops that make their own.