This is going to sound snobby, but it has been at least 10 years since I have had a bottle of commercial salad dressing in my fridge. I find them messy, expensive and odd tasting. Besides, with salad dressing being so easy to make, I prefer to make my own on the spot.
Of course, everyone knows that a bit of good olive oil and vinegar goes a long way, but truly, all salad dressings are almost as easy! My cheat is to buy the premixed salad dressing seasonings from a quality spice shop (The Spice House in Milwaukee has some great choices). From there, I simply add oil and vinegar (for Italian or vinaigrette) or a creamy base (such as mayonnaise, sour cream or yogurt) and milk for the creamy dressings.
If you are inspired now, check out The Spice House's website for an amazing variety of more intricate dressing recipes such as hot bacon, honey mustard, chai dressing and chocolate dressing!