Okay I don't know the actual quantities of the stuff because I make it without measuring but here's a money balsamic vinagrette.

olive oil
balsamic vinegar
deli/spicy mustard (the kind with the grainy stuff in it)
fresh ground black pepper
salt

Take a mixing bowl and pour in some olive oil, some balsamic (not quite the same amount as the oil) a couple spoonfuls of mustard (or squirt it in if it's from a squeeze bottle). Grind in some pepper, sprinkle some salt. Mix it up with a wisk and yer done. The ingredients should be combined but you don't want to whip it up--the texture should be nice and light.

You can also do a variation of this with dijon mustard instead of deli mustard where you whip the oil and then add the vinegar then the mustard while wisking the whole time. It makes an emulsion, i.e. it's kinda thickish like mayo.