Wizard
1. Blink
2. GroupTeleport
Utility utility utility. I wanted to put port up here too, but well, just isn't enough space. The ability to bring your entire party to an inaccessible area is huuuuge. There just anything else that beats it.
Necromancer
1. Web
2. Poison
Ninja
1. Backstab
2. Envenom
Backstab is awesome. With the help of backstab, I am able to deal an insane amount of burst at the start of a fight. Every single click is a burst of damage unlike anything anyone has ever seen. Combine this with Envenom, I am able to achieve so many backstabs per second it's almost unreal. I've even been deemed a hacker on several occasions due to this. They just don't understand how much damage a Ninja can deal when he uses his abilities properly.
A Ninja can't always win a face to face confrontation, but if they get the jump on you, there is no survival. You're dead.
Ranger
1. Track
2. Ice Arrow
Tracking is the backbone of roaming world PVP right now. If you're looking for action, and you don't know where it is, you need a track. It allows you to skip the BS searching and head straight for your goal.
Ice arrow is the bread n' butter of the actual class combat. Without it, they cannot hope to even participate in a fight.
Dragoon
1. Jump
2. SuperJump
Dragoon can go anywhere and do anything with the help of these two abilities. It's what makes the class. What they lack in combat abilities, they gain in world traversing. They can use these advantages to actually gain the edge in combat, which is always really fun and rewarding.
I just couldn't see it being the same class without these two abilities.
Samurai
1. Windwalk
2. Disgrace
Windwalk is...amazing. It's no coincidence that the moment the class recieved this ability, a large number of Samurai's started popping up all over the server. It pushed them from a slightly above average skirmisher to the top pvping class holder. It gives them the ability to close the gap, but also gives them the ability to take advantage of their overbearing DoT effects.
While I personally think that it's the combination of Disgrace + Mortal Wound that brings the umph to the fight, disgrace is probably the more important of the two. This DoT lasts for freakin AGES, and ticks at a pretty fast speed. Samurai's are able to use this ability to gain more left clicks in every fight. Truly, their damage is only limited by how fast they can click due to the insane amount of DoT ticking that occurs on their target.