World of Warcraft Spotlight
With this addon you will get more insight in your debuffs; as a result, you will not have to worry anymore about casting them too late or too soon. Upon attacking an opponent, DOTMonitor displays the icons of the spells that you are able to cast. Once a debuff has been applied, its icon will disappear, until the effect is almost over. At that moment, the addon will emphasize the icon again to notify you that you have to cast the spell once more.
Besides telling you when you can use certain abilities and spells, you will also be told when you are unable to; due to lack of mana for example. This is done by displaying grey icons rather than coloured ones.
In addition to the icons explained above, there is also an option for numerical timers. You can choose from an active effect timer, cooldown timer or both. These features, and various other ones can be configured easily by using the included commands.
Simply clicking the "Install via Curse Client" button found on the addon page is all you have to do to install this addon.
DOTMonitor is a very useful addon if you are interested in having more control over your debuffs. It will tell you when you should cast them and when you are unable to. And you can also configure the addon to your liking.