It's better known as Ranch (which is a Hidden Valley trademark), but Buttermilk dressing is the original name of this American classic. And when you make it yourself, the freshness of the herbs and buttermilk really makes the whole thing sing (plus there's no MSG).
For a different kind of dressing, skip all the seasoning except salt and sugar, use lemon juice in place of vinegar, and add grated lemon zest and lots of fresh herbs: marjoram and lemon thyme, say, or tarragon. Or try the mayo-buttermilk base with garlic and lime zest and juice along with cilantro, and you will end up with the perfect dressing for a Mexican-style salad with black beans, corn, tortilla chips, and grilled chicken.
Whisk together all the ingredients and serve as a dip or dressing. It keeps well for a few days or so, but after that it starts to taste like aging garlic: halve the recipe if you don't plan on using a ton of it right away.