Usefull for most classes :)
Forecast (http://www.curse-gaming.com/en/wow/addons-3948-1-forecast.html)
it lets you see what is being cast on your target, and what is being cast on you, by those that have this Add-on installed.
Note that you need to have it installed for others to see what you're doing...
It will be very good for conserving mana. also for seeing Battle Resses and so on...
May i recommend all to install it, im using it from now.
Will download it and install it to give it a try after the raid :)