Bartender4 - a full ActionBar replacement mod. It provides you with all the features needed to fully customization most aspects of your action and related bars. Includes an out of range indicator for buttons.
Buffet - generates macros that will put the best food/water available into a button, the buttons will automatically switch to health and mana potions when in combat. You can press shift to see bandages.
Clean Icons - Mechagnome Edition - replaces the default Icons with a better look.
ClassicSpellActivations - Lights up spell activation overlays for reactive abilities like Overpower for Warriors.
LiteButtonAuras - Shows your buffs on you and your debuffs on your target inside your action buttons with a colored border and timer. You can see an example on the Blessing of Might in the image.
OmniCC - adds cooldown text to any button with a cooldown. You can see the cooldown on Lay on Hands in the image.