i used ToToT for 2 things. to make sure which target the boss has (when raiding) and also to make sure that the MT/MA has the same target as me (in fights with multible mobs/bosses). As a Healer its even more necessary since you usually have the MT targetted and you need to check how hes doing with aggro (or if the boss changed target to a squishy clothie).
Since I haven't seen much here about pvp/arena addons here are the only ones I use and have obtained a 2400 personal and team rating.
Nature Enemy Castbar (NEC): A good castbar addon that keeps track of all cooldowns used by everyone around you. If you learn to use it correctly it can definetly mean a win over a loss.
Proximo: An arena addon that is very basic but nearly 100% necessary for synchronized play with your team mates. It creates bars for every enemy that you or a teamate targets (up to 5 in a 5v5). The bars are color coded for their specific classes. The bars show the health in real time of every enemy. You are also able to simply click on the appropriate bar to target them allowing easy target switching.
Healer specific addons:
CTRaid: This can be any raid interface helper that you want. I use CTRaid because it shows exactly what information I need/want to know, in a very simple fashion with very little clutter. If you configure it right, you can have it show exactly what information you want. First and foremost it shows all of your party members health (mana bars are optional). Second you can configure what buffs you want to be aware of on every aprty member (up to 4 with priorities set). This is very useful if you want to glance quickly if your hots/buffs ect have faded. Finally, I find it the best decursing helper in the game. You can configure it to where the name of the person who gets a curable debuff on them turns bright red, then shows the debuff on the normal buff table. Many people like using specific addons/macros for this, but I find I am quicker than those addons and more alert of other situations.
Caster Weapon Swap: This is a nifty little addon that if used properly can help tremendously with mana problems in long fights, especially in 5v5 competition. The addon's main purpose in arena is to automatically swap two sets of main hand weapons, specifically one with the enchant "Spellsurge" on it. Spellsurge is an enchant that grants 100 mana over 10 seconds to every person in your party. The proc rate is extremely high (somewhere like 50%), but the proc has an internal cooldown of 50 seconds. The addon automatically detects the spellsurge buff, and changes the weapons directly after a cast is initiated. This is important because swapping weapons generates the GCD, but you can swap weapons while GCD is already initiating, so with this addon you will have no impact on the amount of spells you can cast from GCD downtime. If every caster or simply healer in your party has this enchant/addon it is similar to having a static +70 MP5 per person. Very game breaking.
Gregormi, do you have any melee weapon swapper addons? If not, I'll just write up a macro for it.
And I assume Carloseus isn't going to remove the condescending green from the first thread?
No, I am not. My thread, those are MY personal recommendations. The others are there if people want to try them out, but the ones in green are the ones that work for me, and that is there for people who are less eager to try out every single add-on that's up there.