"Recipe Radar assists players in finding recipes. It knows about vendors who sell recipes in the current region or by profession. It has a number of filtering options and can even locate vendors on the world map."

There are many "hidden" vendors offering recipes. Even at lvl 60 i am still missing some recipes just because i did not discover such vendor - this add-on is a wonder. It lists all recipes available from vendors and shows a location of such vendor. And as you can filter out recipes you have, it's easy to acquire missing recipes. It even helps to find recipes for your alts - that way you can pick up recipes with your main and just send them to your alts any time.