I hate having to give exact amounts of stuff... I mix stuff purely on taste, and on the ratios that I just somehow retain in a scary part of my brain... so I will just explain how I came up with this dip to the best of my ability.
Take a 16-oz cup of Sour Cream (regular on down to fat-free, and even low-fat yogurt would work... take one packet of your favorite onion soup mix and one packet of ranch-flavored powdered mix (Lay's makes a good one).
Mix equal parts of each mix to the sour cream, TO TASTE. Some may like a lighter flavor, some may like more. Start with a teaspoon or so at a time and add it in as you see fit.
I just find that the combo of flavors is perfect... tastes awesome on tortilla chips, Baked Lays, regular chips, and Triscuits, from my experience. I'm thinking of adding in another ingredient for a variation, but I'll have to get back to you on that!