I really like fat-free cottage cheese and soft fat-free cream cheese. They don't have any sugar added. Just today, I mixed some store-made ham salad with an equal amount of soft fat-free cream cheese. The cream cheese has xanthum gum, a thickener, and one thing I don't like so much is the slight 'gummy' texture it can give a product. It tastes fine, however. The ham salad actually tastes BETTER to me with the non-fat cream cheese added. There isn't much of that xanthum gum texture when it's 'diluted down.'
Fat-free Greek yogurt is also tasty. And fat-free sour cream to me tastes a bit like fat-free yogurt.