Druid tanks: Maximum HP
Druid tanks are known far and wide for their massive amounts of HP. Nobody else can come close, and with the Icecrown Citadel buff boosting HP by 30 percent now, druids can survive a few hits from any boss. Their high life also makes them good tanks against magical damage, where there's very little mitigation possible. As a holy paladin, I love healing good druid tanks. While healers with a lower capacity of healing per second (HPS) may hate how much healing they can require, holy paladins have HPS in excess.
Because of the amount of life we have to heal up when they take a hit, we're locked into using Holy Light to keep one up. Flash of Light simply doesn't produce enough HPS to keep one alive on a difficult fight. One note about feral druids is that they
don't currently have an interrupt have a long cooldown on their interrupt, so I like to stand with my feral tanks and use Hammer of Justice to help them out if their target is casting. Even us holy paladins have a few protection abilities at our disposal, and we can use them to augment our current tank's toolbox.
Their damage reduction cooldown, Barkskin, is fairly weak when compared with the other tanking classes. This means that they'll appreciate Hand of Sacrifice and Improved Lay on Hands even more, so be sure to ask when they'd like for you to help out. Their pseudo-cooldown of Frenzied Regeneration and its glyph would normally be pretty weak, but holy paladins are able to take full advantage of it. Since their life pool is so high, we can actually throw critical Holy Lights at them when their buff is active and still not have any overhealing. It's sort of like healing Valithria, where there's no overhealing and so we're getting the full effectiveness out of each heal. Holy paladins typically have the most overhealing, and druid tanks can help alleviate that.
Death knight tanks: Cooldown for every job
Death knight tanks are the masters of the cooldown game, and each one of their specs has its own flavor of cooldowns. This means that they typically have some trick up their sleeve for every powerful boss ability, so you may not need to use your external tanking CDs like Hand of Sacrifice or Divine Guardian as often. As they were designed in Wrath, after the other tanks had already settled into their own niches, Blizzard designed DKs to not have any inherent weaknesses. They've got every variety of taunt, cooldown, interrupt, and other ability that a tank could want. About the only thing they don't have is a gap closer or movement speed boost, so be sure to toss them a Hand of Freedom if they're stuck somewhere.
Knowing which spec your death knight tank is currently playing is important now, though in Cataclysm, all DK tanks will be blood specs. Blood tanks require extra healing when they use Vampiric Blood, while frost tanks will require less healing when Unbreakable Armor is active. Death knights tend to have lower avoidance than the other tanking classes, and so they'll be getting hit on a pretty regular basis. They also don't have any avoidance cooldowns they can use, so you can count on them taking damage all the time. If you're healing two tanks, put Beacon of Light on the death knight. That will ensure that they've always got the healing that they'll need, even if you toss a heal to a raid member.
Warrior tanks: Jack-of-all-trades
According to Matthew Rossi, our resident warrior (and tanking) expert, warrior tanks have two strengths: they're good (but not great) at everything, and they have the most flexible toolkit. Warriors have similar avoidance to a druid or death knight via dodge and parry, but toss on a whole bunch of block from their shield as well. Warriors also have the ability to double the amount they block for, via Critical Block. This makes them great tanks for any fast-hitting enemies, as their shield will mitigate a ton of damage. Warriors were the only tanks that could pull off solo-tanking the adds on the Anub'arak encounter in Trial of the Grand Crusader, due to the sheer power of block and Critical Block.
Warrior abilities, while potent, also have long cooldowns attached. They'll be happy to receive Hand of Sacrifice or Divine Guardian while waiting on their own CDs. Their CDs are powerful enough that they don't need to be stacked with one of ours, so be sure to coordinate so that you and the warrior take turns using CDs. Healing a warrior tank can be unpredictable due to their blocks, as they can take almost no damage for a few seconds and then get hit for full damage several times in a row. Don't fall into the mistake of assuming that a warrior tank won't need any heals, as you always want to be prepared in case they hit a string of bad luck and don't avoid any attacks. Warriors are also very mobile due to Intercept and Intervene, so I like to toss a Beacon on any warrior tank that will be doing a lot of running around, in case they end up more than 40 yards away from me.
Paladin tanks: Automatic cooldown
You're a paladin, so you should already know everything there is to know about paladin tanks, right? Well, I'll go over them as a refresher anyway. Protection paladins have the highest avoidance and mitigation combination of any of the tanking classes, and can actually become unhittable due to Holy Shield. On a recent Deathbringer Saurfang parse, my raid's paladin tank was never actually hit. This means that they'll be taking damage in a fairly smooth basis, so you'll be focusing on keeping them healed on a similarly consistent basis. Paladins are unlikely to take any spike damage, which is nice for healers.
Paladins also have a healer's best friend, Ardent Defender. Even if we make a mistake and miss a heal or two, or the tank makes a mistake and misses a cooldown, paladins get a Get Out of Jail Free card. Ardent Defender will bring them back to life once every 2 minutes, meaning that every paladin tank has an extra 35 percent life just waiting to be used. When combined with the fact that paladin tanks take fairly consistent damage, it's very hard to lose a paladin tank. A paladin can also have two different damage reduction cooldowns, via Divine Protection and glyphed Hand of Salvation.
I usually tell paladin tanks to use their own Sacred Shield, and I toss my Sacred Shield onto the other tank. That way, there's two targets shielded, and I can proc the Infusion of Light FoL HoT on both of them. I also like to use my Beacon on non-paladin tanks, since paladins aren't typically the type to do a lot of running around. They've got solid ranged threat and no instant gap closers, so I can keep them in range most of the time. Some paladin tanks can use Divine Guardian themselves, so try to coordinate with them to alternate usage. One other trick I've used to help out paladin tanks is to use Lay on Hands to give them some mana if they run out. I guarantee that they'll appreciate the help.
The Light and How to Swing It (Holy Edition) helps holy paladins become the powerful healers we're destined to be. Learn the ropes in Holy 101. We can help you keep a tank alive, heal a raid when necessary and beat the global cooldown. Tanking is a job, DPS is a craft -- but healing is truly an art.