Have you tried making your own dressings?
Something like this maybe?
2 tablespoons honey
1 tablespoon dijon mustard (whole grain dijon is also great if you have it)
1/2 teaspoon salt
1/2 teaspoon ground pepper
1/4 cup balsamic vinegar
3/4 cup extra virgin olive oil
1 garlic clove, crushed (or minced if you like a stronger garlic flavor)
Making it yourself will give you loads more control over the calories going into it, if you want it less sweet, don't add as much Honey, or sub the honey for Agave, the possibilities are endless!
My favorite "low cal" not home made dressing is the PC Blue Menu California dressing tho