Because of a stealth change in the latest patch (1.3.3) this will NOT longer work !!!!
In specifics i am talking about the Point Defense Drone.
I am opening this thread because most players are unware of the PPD not only blocking Muta and Corrupter attacks, it also destroys Broodlings. It is not even mentioned in the Liquipedia!
This mighty creature is the fear of every terran and indeed it is a powerful unit. It not only has a 20dmg attack with range 9.5, it also spawns Broodlings which can attack on their own. On the first attack a Broodlord spawns 2 Broodlings, then one after the other.
This is especially fearsome for a terrans with Siege Tanks because they will automatically target the Broodlings and so the terran will damage his own units. Also movement of units (e.g. Thor) gets slowed down. If the terran unsieges the zerg will attack with the rest of his units easily rolling over the terran army.
Allthough Ravens are powerful spell casters they are used most of the time solely for detection purposes against burrowed banelings, some terran players even don't build them at all.
Point Defense Drone
The PDD is immobile and cannot attack, but will negate specific enemy projectiles near itself. Used against Broodlords it will block 20 Broodlings from spawning. The Broodlord still deals 20dmg but the units can walk freely and won't be focused by tanks, so the tanks can remain sieged.
1 PDD blocks 20 Broodlings.
1 PDD block Broodlings from 1 Broodlord ~ 1 Ingame Minute
2 PDDs block Broodlings from 6 Broodlords ~ 20 Ingame Seconds
4 PDDs block Broodlings from 6 Broodlords ~ 40 Ingame Seconds
4 PDDs block Broodlings from 10 Broodlords ~ 20 Ingame Seconds
How to use it:
Many highlevel Terrans are already incorporating the Raven into their play mainly because of the devastating Baneling bombs. So instead of getting 1 Raven for detection purposes i recommend building 2-3 Ravens. Each Raven can build 2 PDDs when they have full energy. Even if the zerg doesn't get any Broodlords the Raven still remains useful as harrasment unit (AutoTurret) and damage dealer (Seeker Missile).
This will most likely not revolutionize the whole ZvT Metagame, but on higher levels some battles can be turned into the Terrans favor, deciding whole games. Especially the Thor with his range 10 air attack can easily battle the Broodlords from the distance without taking too much damage.
Edit: Of course vikings are (and will still remain) the main answer to Broodlords. But the Raven (if built beforehand) can help you out immensely.
Tip: You should always throw down at least 2 PDDs because the first attack from a Broodlord will spawn 2 Broodlings