HealthQuake
It might not be the most practical combat maneuver (knocking your allies prone and healing them?!), but it looks fantastic. The green tint and windy execution never fails to deliver.
Combination: DDDDW + Shift + Right Click

Firestorm
This one takes a combo of two different elemental groupings. First, cast a flaming wall of rocks using FDE + Shift + Right Click. Second, cast a massive ball of fire on yourself by using FFFFF + Shift + Right Click.

Type II Supernova
Quick -- what elements does a Type II Supernova displace? Answer: QSSSD + Middle Click.

Red Light District
A flick of the wrist, crack of the staff, and a hint of arcane power yields an overwhelming urge to start a rave party. Or, at least, that's what DDDSS + Shift +Right Click did for us. Yeah, we're normal.

Fireworks
Landmines are fun. They're especially fun in the form of water, arcane, and shield elements -- SQSQE + Shift + Right Click produces a barrier of watery, arcane-y mines that will ensure the death (or, at least, dazzlement) of your enemies!

Stalagmagician
Your enemies will never again forget the difference between a stalactite and stalagmite after this concoction.
Combination: RQRQRQRQ + Shift + Right Click

IMA FIRIN MAH LAZARS
You knew it was coming. Space_man came across the discovery of combining frost shards with electricity and arcane and its devastating output. RQRQRQAS + Right Click will spray electrified frost shards like machine gun fire.

What are your favorite combos? Put your element combinations in the comments below!