Ever since I figured out how to make a decent vinaigrette I haven't bought salad dressing. My favourite is a Balsamic vinaigrette:
3 tbsp olive oil
2 tbsp balsamic vinegar
1 tbsp whole grain mustard
S&P to taste
Switch up the vinegar and add herbs, onions, whatever you want, and it changes to match whatever type of salad you want to make. It's so easy to make and there are no strange chemicals in it.
I do the same and add a little honey to it.
My favorite bottled dressing is Hidden Valley Ranch original.