I know the Warlocks get the Rain fire or something spell at 20, and i was wondering, does it equal or come close to the mages AoE? Which other AoE spells do warlocks get, and what lvl?

You're on thottbot posting.  All the spells are listed.  Check them out and compare. 

Im asking in others' opinoins. The stats on everything dont tell exactly how powerful it is.

warlocks have 3 aoe spells that're worth discussing in terms of dps.
rain of fire
hellfire
seed of corruption

rain of fire isn't as good as mage aoe.

hellfire is better but you take as much damage as the mobs do so you need some major healing for it to be anywhere near useful. it's powerful but impractical

seed of corruption is the best aoe in the game, beating everything mages have but you only get it at 70.

if you have a pally tank who is aoe tanking, seed of corruption will put even a badly geared lock at the top of the meters.
basically, lock aoe loses until 70

SoC > Mage spells > your other AoE

i disagree I love rain of fire!!! I am a lvl 62 human lock and when my felguard is getting hammered I use that and it does work pretty well. I am not sure about mages. But I think that it is worth it to use it when needed.

It is good, but Seed of Corruption is 10 times better.

yeah, rain of fire is fine. the more mobs you can cover in the effect the better, obviously, but it's essentially just like mage aoe.

once you get to lvl 70 and run shattered halls with a paly tank, you'll see just how effective seed of corruption can be. i tend to do 50% of the group's damage on a SH run and have a dps upward of 1600 (with decent gear but nothing special)

Causes chaos in AV bridge too.

There's probably a mod (and I'd make one if I could, but I don't know how to) that targets anyone with a SoC on them and spams dispel like crazy.

But of course with the crazy amount of incoming damage (even from the seed itself) it goes off pretty fast.

surprised me how long it can take for horde to realise you're seeding like crazy hehe - watch the numbers fly! 
Once they have realised tho they are really on the lookout and will go all out to get you :(
(do they make a macro to target the lock especially I wonder?)

With the macro you made in the other thread (the one with all the focus and stuff) you could make on that targets the Lock (and the target is changeable), and if you press alt and the macro it goes /targetlasttarget, and so you can choose to interrupt/silence him , and if he isn't SoCing anyone, you just alt+macro to go back to the last target.

Would that work?

yea....SoC is hands down the best

Does SoC benefit from the Improved Corruption Afflic talent?  If so, does it allow for at faster "seed affect" and does it stack with the AOE after affect on others???

improved corruption does not affect SoC (that would be imba), neither does empowered corruption. contagion, however, does affect SoC damage.

don't gear specifically to improve your SoC but more +dmg and more +crit will help it to do more overall damage.
the biggest problem with SoC is that each seed can only do about 18k damage. there'll be a few pulls where you have LOTS of mobs in the effect (espeically if you run with pally tanks much) if there's 30 mobs then they can only take a maximum of about 600 damage so you'll need to put more seeds in the pack.
basically, if everything is tanked then just keep doing [tab] > seed > [tab] > seed etc until everything's dead

ur forgetting dest talent Shadowfury

It scales horribly and is not spammable.

yeah, what bananaz said. shadowfury isn't a damage spell it's a stun that does a a bit of damage