Not sure about low fat, but here's my best soup recipe!http://tails.co.za/2009/03/recipe-homemade-soup/
Otherwise here is one of my Weightwatcher's recipes:
Tomato and Veg soup:
Serves 2, Prep. & cooking time: 20min
500ml stock, made with stock cube
250ml tomato juice
100g bean sprouts
1 tablespoon of peas
1/2 small cauliflower, broken into sprigs
1 celery stick, sliced
Tabasco or Worcestershire sauce, to taste
Place everything (except Tabasco/Worcestershire sauce) in a saucepan and bring to the boil and simmer until the celery and cauliflower are cooked.
Add Tabasco or Worcestershire sauce.