This may have or may not have been posted before, I did a search and it returned no results anyhow, some of you may already know this some might not.
This lil exploit will allow casters to cast faster (only slighty but u can feel the difference).
For this you will need to download the addon (note this file is linked to files.wowace.com so nothing funky), and install it.
Now load up your caster and you will notice that your casting bar has been changed by this addon to a fancy new one, you will also notice that the casting bar shows your ping in a red bar at the end of the casting bar, this is what where going to focus on.
Basically if you have your for example Fireball hotkeyed to number 2 on your keyboard, when the casting bar reaches the bar showing your ping you hit your number 2 hotkey again, and just keep doin this untill youve nuked your mob down, and you should notice that you now have faster casting.
Enjoy!