I'll give a few guidelines for creating your own FF salad dressings,
then a couple of samples that have worked well for me.  These recipes
make dressing for two people.  Dressing is very forgiving, and if it
tastes odd, it is easy enough to fix.

Vinegar Base:
I generally use balsamic vinegar as the base for salads when the rest
of the meal is european-style.  For indian, middle eastern, and asian
meals, I use brown rice vinegar, which I get at the local ethnic-food
store. Otherwise, you can use apple cider vinegar.  I don't use white
vinegar, since I like a little flavor with my acidic foods :-)  Start
with about 1/4 cup of vinegar.

Herb or Spice:
If you want to use an herb, fresh ones are the best.  Otherwise,
dried will do.  I tend to use herbs and spices traditionally used in
the style of cuisine I am preparing.  Add a total of 1/2 to 1 tsp of
herbs and spices.

Sweetener:
This is entirely optional, it just adds another dimension to the
dressing. Use a flavorful sweetener, like honey (I've never tried
brown rice syrup or malt sweetener, they'd probably be great).  Table
sugar will add sweetness, but, like white vinegar, little flavor.  Use
about 1/2 tsp of sweetener.

Mustard:
This, again, is optional, but a nice touch.  Don't use yellow mustard.
Stoneground and Dijon mustards are tasty.  Use sweet hot mustard in
asian-style dressings.  Use about 1 tsp of prepared mustard.

Water:
This will tone down the dressing a bit, if you like to dump a lot of
dressing on your salad.  I generally don't add water, but then I only
dribble a little dressing over each bowl.  The dressing is very
flavor-saturated, so it actually will spread over two bowls of salad.
Add about 1/4 cup of water if you want to use it.