I'm trying to avoid vegetable oils, and I've experimented wtih sour cream-based salad dressings.

This one's pretty good: mix in a bowl 1/2 t mustard (I use organic yellow mustard), 1 t vinegar (I use sherry vinegar), and a few drops of lemon extract. Add 1/2 cup of sour cream and mix well. You can add garlic, shallots, sesame seeds, turmeric, or other herbs; also add a little more vinegar or mustard, depending on how tangy you want it. Works well as a dip also. May want to add a little half and half for thinner consistency as salad dressing.