or do you just use caramel sauce that come in a jar or plastic bottle to be poured over ice cream?
I use caramel frosting itself as a filling.
I've tried the Duncan Hines ready-made caramel frosting. If you like butterscotch...it's delicious but it tastes nothing like caramel. You might also try using caramel apple dip. That tastes so good. I've never used it as a filling but I've seen recipes where it is part of the filling (I think the Snicker's cake Dawn shared uses it).