Well of Darkness + Churning Earth = Rockin' AoE Damage
Professions: Necromancer, Elementalist
"This is a brutal combo. A necro can use Well of Darkness to create a Dark Field, which blinds enemies in the area. Along comes an elementalist attuned to earth, who cast Churning Earth to cripple enemies inside the Well of Darkness. When Churning Earth ends, it combines with the Dark Field to deliver additional AoE damage. Guaranteed to rock your enemies world – in a bad way."
-Ryan Diederich, Programmer
The Ranger -- capable of creating their own combos.
Contagion + Ricochet = Poison Axe to the Max
"Rangers can choose some strange but useful pets, like the Murellow, which is kind of a diseased rat/bear that lives in the caves of Tyria. The unhygienic Murellow uses a skill called Contagion, which creates a Poison Field. An axe-wielding ranger can then use his basic attack, Richochet, to throw projectiles through the Poison Field. The axe ping pongs between enemies, applying Poison to a number of foes."
-Eric Flannum, Lead Game Designer
Smoke Screen + Stomp = Cloaks for Everyone!
Professions: Thief, Warrior
"This is one of my favorite combos. You take a thief, who uses his/her Smoke Screen skill to create a smoke field. Then a warrior comes along and blasts the smoke with a Stomp, adding Stealth to nearby allies by cloaking them in gloom. It's a very cool effect, and it comes in handy in combat."
-Ben Miller, Game Designer
Symbol of Swiftness + Big Ol' Bomb = Blindness Bomb
Professions: Guardian, Engineer
"A guardian can lay down a Symbol of Swiftness, which creates a Light Field on top of an engineer's Big Ol' Bomb that is about to explode. This will add Blindness to the explosion, effectively turning two offensive skills into an AoE defense!"
-Andrew McLeod, Game Designer
The Mesmer's clones and illusions use combos for a lot of their utility.
Healing Spring + Unload = Bullets that Heal
Profession: Ranger, Thief
"The skill Unload is one of the best ways to put out a ton of damaging projectiles, but when you combine it with a ranger's Healing Spring, you get a completely different effect. A ranger creates a Water Field with his Healing Spring skill, which a thief can then Unload through. These healing projectiles grants an area-of-effect heal to any allies that are attacking the thief's target. This healing doesn't apply to bad guys. This combo is one of the best ways to add some healing to an ally who is deep in hand to hand combat."
-Matt Pennebaker, Game Designer
Chaos Storm + Rapid Fire = Crazy Arrows
Profession: Mesmer, Ranger
"When a mesmer fires off Chaos Storm it grants random boons on allies and random conditions to any enemy within the effect area. You ranger ally inside the Chaos Storm can fire through the field, applying Confusion to each enemy he hits. Chaos!
-Jonathan Sharp, System Designer
Lava Font + Leaping Attack = A Burning Sensation
Profession: Elementalist, Mesmer/Warrior
"Here's how this one works. An elementalist triggers a Lava Font near an opponent. Then, your buddy the sword-wielding mesmer or warrior can leap into the Lava Font's area of effect, delivering additional burning damage to the enemy."
-Jon Peters, Game Designer
Frozen Ground + Eruption = Stay Frosty
"All you need is one elementalist for my favorite protective combo. Cast Eruption first, then attune to water and cast Frozen Ground. When the Eruption Bursts, damaging your foes, an Ice Field spreads over the area to apply a protective Frost Aura to you and your allies. I wish I could do this in real life on hot days."
-Karl McLain, QA Tester
Super Elixir + Illusionary Duelist = Condition Eraser
Professions: Engineer, Mesmer
"We call this getting Bearced! An engineer with Elixir Gun fires a ground targeted Super Elixir creating a Light Field. Then a mesmer with a pistol can summon an Illusionary Duelist to fire projectiles through the field, which will remove conditions from allies near the target."
-Tyler Bearce, QA Tester