Vinegar as it is tastes a little too plain to me, so I like to add a touch of sweetener to it. Makes the salad yummier. In my opinion a salad should taste like something, otherwise it is boring to eat. Just need to remember to not overdo the sweetener part...
I usually mix my own salad dressing for each salad I make. Just add things together in a tiny cup. That way you get it just right for your salad and current mood, just as fluidy as you want it, and you know exactly what is in it.
I wouldn't buy any salad dressing from the store...
Also, using the tiny cup, you know how much of it you are making/eating at the time. The 2 or 5 kcals it adds to the salad is a small cost for making you want to eat it, and enjoy it.
here are my simple favourites for dressing:
vinegar+sweetener
lemon/lime juice+sweetener
mustard+milk+vinegar+sweetener
curry+youghurt(+milk)+chutney or somethign else fruity
hot chili sauce+milk+sweetener