Asda have a lovely honey and mustard dressing from the "good for you" range. Really tasty and only 16 cals per tablespoon! Or what about making a low calorie coleslaw with extra light mayo (recipe on recipe thread)
I think it's called hellmanns fat-free vinegarette, It doesn't taste vinegarry, and obviously has no oil. But I think it's delicious. 7cal per serving I think.. I really love it.