After the changes to threat a few weeks back, tanks have rarely had threat issues at the raiding level. In my experience, it's never really been about raiding threat, but changing threat across the board meant that threat management was just one less thing to worry about. You still need to build threat as a tank, however, so don't ignore your rotations just yet.
Addon threat meters, ironically, are not about watching your threat relative to the DPS players anymore. Rather, on fights where two tanks are sharing tanking duties, you want to watch your threat so that you do not pull aggro off of the other tank and reset a stack of debuffs or take an otherwise undesireable special hit. Baleroc and Ragnaros, for instance, are both fights where tank swapping during critical moments is a big deal and crucial to making the fight go smoothly, and a threat meter can help big time in keeping your threat where it needs to be.
Omen and Skada are the two big boys in the threat meter game. Many people like Skada because it doubles as a DPS meter and damage parser, which is great for dual-spec tanks who dabble in DPS. Either way, having Omen installed anyway is probably a good idea even if you don't use it. It is still the most comprehensive threat package. While threat's role has changed and its emphasis lessened, the mechanic still exists in game and you would be wise to watch it.
Download Omen Threat Meter at [Curse] or [WoWInterface].
Check out my Addon Spotlight article on Skada.
Communication is key
Tanking these days is all about keeping a boss on you, mitigating the damage being done to help save healer mana, and making sure the boss is where he is supposed to be. For job #2 in that list, you're going to want an addon that announces when you use your big cooldowns as well as when they expire. Communication wins fights, and if an addon can help with that, I'm all for it.
With the Raid Finder, communication will be at an all-time low. People are not going to have the luxury of immediately being put into a Ventrilo or Mumble voice chat room together, and unlike dedicated raiding groups, people all don't have the same communication setups. Communication is a hindrance and hampered at the start in a Raid Finder setting. All you've got is text.
Spell announcers are a great way to help with this. I personally recommend Raeli's Spell Announcer, which allows you to set your cooldowns to announce to a "smart" channel, meaning your announcements will go to a raid channel if you are in a raid, a party channel if you're in a 5-man, etc. It's a nice feature and makes it so you do not have to set up a macro for every cooldown and tailor it specifically to your channel setups. The addon knows.
Big tank cooldowns are important for everyone to know when they are on and off. Healers can conserve mana, tanks can prevent their own deaths, and even DPS who have raid-wide cooldowns like the warrior's Rallying Cry can use this addon to alert the raid when their cooldown has expired so another player can hit theirs. Communication wins fights so, please, communicate.
Check out my Addon Spotlight article on Raeli's Spell Announcer.
Threat plates and multi-add fights
One of the greatest addons for tanks that I have been using for most of my WoW
career is TidyPlates. In dungeons, TidyPlates is critical. In raids, TidyPlates saves raid nights. Tanks and adds are like peanut butter and chocolate -- two great tastes that taste great together, and Blizzard can't stop eating them. If you're a tank, at some point in your tanking career, you will be grabbing groups of adds and holding threat on them -- Maloriak, Rhyolith, etc. The fights are there, and they aren't going away.
Why is TidyPlates so necessary for fights like these? Well, groups of adds and their associated nameplates can get cluttered and annoying. On top of that, you cannot jump between three to six adds quickly, tabbing to check your threat on them all. In fact, that's just dumb. TidyPlates lets you see your threat on a whole group of adds without tabbing around and puts control of the aggro in your hands. If you need more precision aggro, target the guy who you are losing. General aggro okay? AOE, baby. It will save you as a tank. You will thank me, and your raid will love you.
Check out my Addon Spotlight article on TidyPlates
There are of course more addons for tanks out there, but for the most part, this is the core of raid tanking. Communication, threat management, and making sure you know how your fellow tank is doing are the key tasks at play here. Play smart, have fun, and hold that shield up extra high, because nobody likes blood on the healers' hands.
Oh, yeah, and don't forget to get DBM
Addons are what we do on Addon Spotlight. If you're new to mods, Addons 101 will walk you through the basics; see what other players are doing at Reader UI of the Week. If there's a mod you think Addon Spotlight should take a look at, email firstname.lastname@example.org.