This is my evil little mod for the spellbar... gem icons are T.King's Chipped Edge (not included).

As you can see by the screenshot, the skulls' eyes glow on mouseover and book appears.

What you can't see is that when you cast, there are dark skulls behind the gems, and when you don't have a spell in a slot there is a skull with blinking eyes peering at you, reminding you to mem your Fear spell before you decide to pull!