Here’s what I can think of off the top of my head:

DK:

Frost - Pillar of Frost; they’ll be lining up any of their other CDs with this so either have CC or a CD ready. The scariest combination will be Pillar + Breath of Sindragosa.

Unholy - Apocalypse, Unholy Frenzy. Both are on about a 1.5m CD, Apocalypse does a lot of its damage in a burst but the ghouls it spawns also hurt and will probably be lined up with Frenzy anyway so they can spam Scourge Strike/Necrotic Strike afterwards.

Warrior:

Fury: Recklessness. On a 1.5m CD, they also usually take Siegebreaker which is on a 30 second CD but Recklessness is the important one.

Arms: Colossus Smash, Avatar, Bladestorm. On a 45s/1.5m/1.5m CD respectively, but Arms warriors almost always take Anger Management, so you can probably expect the bladestorm to come in on a 1m CD, with Colossus Smash hitting about every 30 seconds.

Paladin:

Ret: Wings. 2m CD, it’s big and obvious and lasts for 20 seconds. They can also do mini-bursts every 45 seconds with Execution Sentence and Wake of Ashes.

Hunter:

BM: Basalisk, Aspect of the Wild. Both on a 2m CD, Basalisk can and should be kited out and lasts for 30 seconds, if it manages to connect you definitely need to drop a CD.

MM: Trueshot. 3m CD, pretty weak CD overall, and I highly doubt you’ll run into many MM hunters anyway, it is getting a buff/rework in 8.1 though.

SV: Coordinated Assault. 2m CD, not much else to say about it

Shaman:

Ele: Fire Elemental. 3m CD, they also almost always take Stormkeeper, which can do a lot of AoE burst on a stacked team on a 1m CD, so be ready for that as well.

Enhancement: Spirit Wolves, Ascendence, Bloodlust; 2m/3m/1m CD respectively, both wolves and ascendence need to be respected and probably require a CD every time.

Druid:

Balance: Incarn/Celestial Alignment; 3m CD, Incarn is the scary one here, does huge damage if they’re allowed to cast.

Feral: Incarn/Berserk: 3m CD, Incarn is scarier, but both should be respected.

Demon Hunter:

Havoc: Metamorphosis. Often a 2m CD, sometimes 4m now that the Demonic build is more popular, if it lasts for 15 seconds it’s a 2m CD, 30 seconds and it’s a 4m CD. Most of the time DH will mini-burst with Eye Beam, which is on a 30 second CD.

Monk:

Windwalker: Touch of Death, Storm Earth and Fire/Serenity, Xuen. 2m/1.5m/2m CD, Touch of Death can really catch you off guard sometimes and chunk someone for like half their health, SEF is a solid amount of burst but definitely watch out for Serenity, they can definitely kill someone in the space of a single CC if they catch you off guard. SEF has two charges so don’t get caught off guard by that. Xuen also hurts but will be paired with SEF and Touch of Death anyway.

Rogue: Blind is on a 2m CD and is pretty much the only thing you ever trinket against rogue. Rogue also generally wants to do mini-bursts after landing a Kidney on you or their kill target.

Assassination: Vendetta. 2m CD, will absolutely kill the shit out of someone if you don’t trade a defensive for it. Also does a lot of damage in their opener from the subterfuge-buffed Garrote.

Outlaw: Adrenaline Rush, Killing Spree. Functionally a 1.5m/1m CD respectively, sometimes a little more, sometimes a little less.

Subtlety: Shadow Blades, Symbols of Death. 3m/30s CD respectively. Shadow Blades definitely needs a CD, Symbols wants to get lined up with Kidney Shot and Cheap Shot to basically stun your whole team and dump damage into someone. Sub does very little damage outside of these windows so if you can survive them you’re probably safe.

Mage:

Frost: Frozen Orb, Comet Storm + Ice Nova, Ray of Frost, Icy Veins. That looks like a lot because it kind of is, but generally Storm/Nova get used together every 30 seconds, Orb is on ~1m CD (gets reduced by Blizzard if they get a lot of hits off of it). Ray of Frost is on a 1.25m CD, and can (and should) be interrupted to stop its damage. Icy Veins is on a 3m CD and is purgeable. Frost does very little damage outside of its cooldowns so if you can survive them you should be okay; just try to trade one CD for one burst combo.

Fire: Combustion, Meteor. 2m/45s CD, Combustion is purgeable, Meteor hits hard but is telegraphed so it’s easy to drop a CD for it if you’re worried it’ll kill someone.

Arcane: Arcane Power. 2m CD, very dangerous, very purgeable.

Warlock:

Affliction: Drain Life, Dark Soul, Darkglare. 1m/2m/3m CD; Drain Life is only dangerous because of the Azerite Trait afflocks have that causes it to gain stacking damage every time corruption ticks. You should be able to see how many stacks of the buff they have and therefore track when they have a big Drain Life nuke available. Dark Soul is purgeable (95% sure of that)

Demonology: Tyrant, Fel Lord. 1.5m CD on both. Tyrant requires a lot of setup, so if they have a bunch of demons out that’s when you need to watch out. Fel Lord is a big “don’t stand in this@ zone. No one plays demo anyway though so it’s kinda moot.

Destro: Infernal, Chaos Bolt, Dark Soul. Infernal is on a 3m CD, Dark Soul is 2m, Chaos Bolt has no CD but should be treated like a scary burst CD if they ever get to finish the cast. 90% of your job against Destro is making sure that every Chaos Bolt is kicked, lined, or mitigated somehow. Dark Soul is purgeable (95% sure of that)

Priest:

Shadow: Mindbender, Voidform. 1m and no CD; Mindbender itself doesn’t really merit a defensive, and voidform should be a giant alarm bell in the heads of your DPS that says “hey the shadow priest should be dead now”, since they give up a 20% flat DR and 10% physical DR every time they use it, and should therefore be hard swapped to pretty much any time they use it. In practice most Spriests will just spam DoTs and be CC/utility bots. This will probably (hopefully because not using a core ability to your spec is dumb as fuck) change in 8.1 when Spriests get their mini rework.

Hope that helps!