Add-ons 

USE THESE 7. DO IT.

Announce
Puts important CC and HP stats in party chat
Spellalerter
Allows you to see incoming CC and burst as well as crucial stuff like POLY or CYCLONE, or REFLECT or DEFLECT
Gladius
Amazing tool for watching casts and enemy HP, I use this for fast switches without having to weave through totems and its very clean for seeing things like Aura Mastery and Cyclones
Juked
Let’s you see a timer on the CC that someone cast upon you. When is that next sheep available to my opponent? 2 seconds, ok, not giving him LOS ! — configure it for “smart” so that it only shows icons once used on you.
Tidy Plates
Puts a timer over your opponent’s head — on spells you cast on your opponent like “7 seconds left on chill effect”
Omnicc
Puts timers on all your spells so you can tell your partner EXACTLY when your next silence or stun is coming.
diminishingreturns
Puts a timer over your opponent so you know when you can start another sheep/cyclone/whatever CC lockdown on someone. It’s set at ~18 seconds from last cast by default and you can change that manually.
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others recommended by ppl on arena junkies:
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Gladiminish
Lets you see DRs so you don’t overlap Gnaw with Bash and you know when your druids Cyclone chains are next available, VERY useful for synergy with your druid
X-perl
Makes your UI much cleaner and lets you see disease timers far easier than Blizzard UI.
Snowfall Keypress
Reduces the time for your abilities, I use it on Off-GCD abilities (Mind freeze is KEY, it registers the interrupt that much faster) and AMS etc, VERY Helpful
Leatrix Latency Fix
Reduces packet latency, dropped me from 150 to 50 MS average and allows me to Freeze fakes regardless of how laggy Mind Freeze is to begin with.
Quartz
This allows you to see a focus cast bar above your head, very useful for timing gnaws/strangs/grips/focus mind freezes for interrupts