You can make blue cheese, ranch, ceasar dressing etc, without starch. In all likelihood, if you go to a decent restaurant, the dressing should be starch free, its typically the mass producers of the cheap bottled stuff that use starch as a filler.
As far as ceasar dressing goes, make it yourself, (and probably ok in a good restaurant), as the ingredients only (typically) consist of: olive oil, parmasean cheese, lemon juice, anchovies or anchovy paste, and some use egg. Some also add worchester sauce, this may be a slight bit starchy as it has a soy base to it. I've gotten very good at just asking the waitress what they put in their dressings as of late! don't be bashfull.
Blue cheese: can be all over the board as far as ingredients go, best to make this on your own with some , lemon juice, blue cheese, and heavy cream.
Ranch dressing: dill or chives, buttermilk, mayonaise, lemon juice, dried mustard, paprika, (not sure, but I think mayonaise might have some starch)
Personally, you can't go wrong with a balsamic vinagerrete; just use equal parts olive oil and good balsamic vinegar, one clove chopped garlic, one tabelspoon of honey, salt and ground black pepper ( a pinch of each). If you want to taste even better, add one or two shredded or chopped fresh basil leaves. You can even make it tast BETTER by adding a tablespoon of your favorite mustard (however, I think most mustards have a LITTTLE bit of starch in them, tread carefully with the mustard.....but wow does it tie the vinagerrete together. I personally have no problems with a little starch, so I can get away with it, but each is different.
