Quark and natural yoghurt.
@Goody, it doesn't really taste of much, it just gives dishes that kind of creamy, dairy texture you need sometimes! I tend to use it most for macaroni cheese. (Basically boil macaroni, mix it with cheddar and quark, add something like cooked onions and cherry tomatoes, then stick it in the oven for half an hour for it to bake. Sometimes I also add wholemeal breadcrumbs to the top for some crunchy goodness!) It is better than natural yoghurt in some dishes because it doesn't separate when you heat it.