i got this from the mage forums, not sure how far it spread, but i find it very useful in higher rated arenas as a mage and im sure its great for any other caster
MagicTrack.zip - FileFront.com
Using this mod, you can track the cooldowns of counterspell and spell lock, as well as other important events.
When you unzip the mod into your addons folder, two gray blocks will appear ingame. The top block shows a countdown timer when a hostile player uses counterspell, and the bottom block shows the cooldown of spell lock.
The mod also alerts you to when your counterspell actually locks someone out, which can be useful against healers using /stopcasting to fake.
It also alerts you to which buffs you remove, and some important gains like CloS and BoP.