There are lots of alternatives if you don't want to use cream. Crème fraîche is one of my favourites as it is very stable in sauces. It tastes very much like soured cream but has a higher fat content. I tend to add a little sugar to the sauce. If you are looking for a lower fat ingredient then try fat free quark. It has a similar tang to soured cream. You could also use milk instead and cornflour to thicken.