A single addon allowing you to effectively track the actions of your opponents does exist, or at least is the most recognized: SArena.
In Burning Crusade Classic, Gladius and GladiusEx do not appear to be available as of the time of writing. Normally, it still works, but if you have a problem, consider deactivating it while waiting for a stable version for Burning Crusade Classic to be released by its creator. Warning: It is possible that the game detects this addon as outdated. The major feature of this addon is that it makes web links clickable in-game, making it a must have for anyone.
Whether they are in your inventory, your spell bar or anywhere else, a countdown is indicated when one of them enters CD, allowing better overall visibility and therefore better management of your character in battles. OmniCC allows you to add text to items, spells and abilities that are on cooldown.