In designing the first major entirely graphical UI the designer had a pretty steep challenge: how to communicate with users accustomed to text based operating systems using a simple graphic. Some have faded into obsolescence, but many of these have informed further GUI development.
Plus, they look great.
The bomb (this was bad) and watch (still used today in iTunes):


An alert box (application required attention) and the original trash can:


And perhaps most importantly, Clarus the Dogcow:
