Starcraft 2 - Protoss vs Zerg - Counters

As usual if you have read my other guides, you have to remember to scout. Send a probe earlier on to check out stuff, and see if they are going for a whacko build or a standard build, and start building counters to it. Protoss also have observers, and they are great scouting tools, and I really find it annoying how if I don't build missile turrets then my base gets about 3 of them stalking every move I do.

Zergling
Zealot + Partial Wall : If you manage to build your partial wall properly, then this is a very good defense against early zergling rushes. This ensures that only 1 zergling can get through at a time, and then you can put 1 zealot to block it up to fight zerglings off 1 by 1.
Colossus : Later game, Colossus can fight off huge mobs of zerglings with their area splash, and they have an awesome bonus damage against light armour, and along with cliff walking and proper micro, Colossus can be a very deadly tool against swarms.
High Templar: Psionic Storm can take out many zerglings within a  couple of seconds, but high templars can also get swarmed quickly, so a guard group with a height advantage will be a good idea. Later you can morph them into archons, which have a bonus against biological units and a nice splash damage.
Sentry : You can use force field to cut off chokes and give your ranged units to take a few out, and if they do not back away, then this temporary wall can do a good amount of damage.
Anything in the air: Because zerglings can't hit air
Roach
Stalker: Stalkers have a bonus against armor, and with blink and good micro, then roaches may not even get close to the stalkers as they have a very low range.
Zealots : Roaches are suspectable to getting swamped, and with charge you can quickly surround them and hurt them.
Immortal : Immortals will cancel out any attack above 10 damage and put it down to 10 damage, making them able to tank up to 10 shots of acid, which normally do 16 damage. Roaches also don't attack too fast, and on top of that, immortals also do 50 damage to armored units.
Observer : Just in case they decide to burrow into the ground.
Anything in the air: Roaches can't hit air.
Hydralisk
Colossus : Have a bonus against light armor, and can hit an area of them, and also have cliff walking to make them more elusive.
Stalkers : Not the best choice, but is good if you got nothing else because they are decent.
High Templar: Psionic Storm is a nice way to kill huge groups of them, and a nice height advantage so they can't shoot back would be pretty nice. Later on Archons can also be morphed and they have a bonus against biological units.
Dark Templars
Banelings
Colossus : They can avoid them with cliff walk, and also can take out many of them before they can do anything.
Stalker + Blink : You keep shooting till they get really close, and then blink up a cliff or something to avoid them for longer. It will be expected that you may lose a few stalkers though
High Templar : Psionic storm again will kill loads of these things, but the High templar is very easily killed so you will need a height or a small security detail.
Anything in the air
Infestor
Observer + Crew: If they are burrowed, then as soon as they are reavealed they are preyyu easy to kill.
Stalkers : Just blink up to them and kill them, or chase.
High Templar: Feedback will be able to get rid of their energy and maybe kill them, im not really sure. Make sure you act first before he neural parasites you.
Mutalisks
Carrier : Carriers are very tank and can take pretty heavy punishment from Mutalisks.
Stalkers : Mutalisks don't do too much to stalkers, and stalkers aren't exactly the best against them either, but they are tougher than them
Phoenixes : Phoenixes have been confirmed as a perfect counter to mutalisks. While mutalisks do 9 damage to the phoenixes, the phoenixes do a better 20 damage, and have higher manoeverability and also able to chase down mutas due to their high movement speed.

Archons: Bonus against biological, and with a nice splash damage, the mutas tend to come in packs, so letting the archon use the splash to its full potential, and they do a nice 55 damage vs biological units.

Corruptor
Stalkers + Blink - Just to get close and chase them if they try to run away, since they cannot hit land units while the stalkers can hit air.
High Templar : Feedback.
Phoenix : Not very sure about this one
Broodlords
Stalkers + Blink : You need to get close to broodlords so that they cannot long range your units and so they cannot run away as easily either.
Phoenix : Broodlords can't hit air, so phoenix is a perfect counter
Carrier : Also cannot be hit back
Void Ray : Also cant be hit back too.
Ultralisk
Void Ray : Void rays cannot be hit back by Ultralisks, and void rays also specialize in taking down units with massive amounts of health, making them a perfect counter.
Stalkers + Blink : Basic hit and run tactics
Dark Templar : As long as they cannot be seen, dark templars do quite a bit of damage to them
Carrier : Cannot be hit back, and they do decent damage.