A tip that I learned from my Dad a long time ago. In making regular butter cream icing; add an unbeaten egg white and a pinch of cream of tartar. This will form a thin, delicate crust on your icing.

Or....there are the cooked icings, such as 7-Minute and White Mountain. Look them up in any cookbooks that you might have on hand....or, check your local library. Think melted chocolate chips or bittersweet can me mixed into these.

Here is a link that might be useful: Seven-Minute Frosting