Gladius adds enemy unit frames to arenas for easier targeting and focusing. It is highly configurable and you can disable most features of this addon.

Features include;
PVP Trinket status
CC timers
Target-of-target display

Also announces the following events to party/RW (not turned on by default);
Trinket announcement – announces when the trinket is used/is ready again.
Drinking announecment – announces when an enemy has started to drink.
Enemies on low health – announces enemies that are about to die, you can set the percentage yourself. *

Gladius can be downloaded from http://curse.com

* Bold text because, embarrasingly, I didn’t realise Gladius did this until I started watching live feeds from AJ. Maybe others aren’t aware either? Hmm…