Was mucking around in the demo while the full game is downloading and found some awesome spell combinations 
and some that didn't quite work out. Pretty fun game so far, multiplayer sounds like its gonna be awesome.
I like casting multiple spells but most single spells are usually better and don't combine well 
 
[right] lightning + arcane + fire 
high damage beam that lights things on fire 
 
[shift] 5x ice (water + cold) 
does 600 dmg in a large aoe 

[shift] shield + rock + fire 
to make a volcano circle around you, trapping monsters in with you and igniting them, then 
[shift] rock + arcane
to dmg the monsters trapped with you 
 
{Rain} 
drenches everyone
[right] shield + cold
freezes all drenched monsters that walk through 
[right] rock + rock + rock 
charge it up on the frozen monsters and crush em, 5x rock does 11k dmg
 
{Rain} 
[self] shield + water 
stops you from getting drenched so u can cast lightning 
[right] lightning (as many as u can queue up) 
chains to all drenched monsters near each other 
 
Failure
[shift] shield 
[right] lightning + arcane + fire 
the shield reflects all beams so if you fire a beam while inside a shield it bounces around inside it 
was gonna trap monsters inside with me and reflect the beam around to create a ball of death 
the beam pretty much reflected back to me and i exploded :(

Shield + Arcane using shift. Ring of mines around you. Glorious limbs flying everywhere when they try come to you.  
 
Although I've killed myself with it a bunch of times, haha.

this sounds epic!
i laughed a bit at the last one :D

ohhhh 
 
{Rain}
[right] arcane + cold 
freeze beam!

[right](Charged) ice+ice+ice+ice+rock 
Giant flying ice rock does some serious damage. 
 
[right] ice + arcane + lighting 
frozen magick shotgun , charge it to have smaller shot radius.  Great for shooting through multiple enemies

[Shift] Lightning + Arcane
Instant high damage AoE.  Good for emergencies.

Rock + Rock + Rock + Rock + Rock = Charge the direct shot for 3,500+ damage and goes through enemies. Alright, I know that's not a real spell combination because it's all rock, but it is great. :) 
 
I really like doing area effect water and then lightning+shield.

Shield + Arcane (mines) is great for multiple enemies. Sends the little guys flying and stops the chargers.
 
Lightning + Arcane. Lightning Beam! Great damage and great aoe.
 
Ice + Arcane. Slowing enemies to a crawl is always great.
 
M60. The thing is a beast. I went through chapter... 4? 5? using only that (except for 2 instances where I had to use spells). It rips through everything in a few seconds.

A few fun ones, especially in "co-op".
 
Player one uses standard Lightening*3, Arc*2 beam
Player two crosses that with Water*3, Arc*2 beam
Large explosion at the intersection of those two beams, amazing for aoe.  Incredibly dangerous for all involved ie: awesome.
 
Rain + Lightening, requires water shield but really good for aoe, and for frying your friends
 
Standard shield (just shield + Self) seems to reflect arcane beams.  Could be useful with dome of death.
 
Healing mines are awesome (heal, shield, shift)
 
A few others I love but people might not have discovered how to use certain elements so I'll put them in spoilers for those that want to be surprised:
 

Has anyone been able to cast meteor shower?  I would assume you hit spacebar to cast it, but I haven't been convinced that I'm doing it right. 

Yeah, it's fire+rock+steam(fire+water)+rock+fire and then space. Not as effective as you'd think it'd be unless it hits someone on the head. After the first time of being hit on the head, I've learned to always shield 3rd mouse after you cast it.

*Ice 
*lightning
*Shield   is a personal favorite, aoe or weapon enchant doesn't matter

What Renahzor said steam arcane lighting x 3 is my bread and butter for making things die. 
 For spell casters a AOE water blast followed by a cold blast freezes them and sets them up for the murderbeam. For everything else the AoE blast of the deathray does the job.
 
Of course later on the enemies are more diverse but itsstill good.

Probably to enhance my sword with 1 arcane and 4 lightning. > Lightsaber.

Stone *4 + Shield  on Self
Haha that gives me enough time to plan any other spell I need 
usually 2*arcane + 3*fire beam

huge fan of rain, then arcane+lightning+frost

I'm still trying to find my go-to AOE spell. Beams are nice but fuck trying to aim in this game.

water+arcane+rock then cold+arcane+rock is my go to aoe when they're further away, u do it really quick and it makes em wet then freezes em, usually kills everything instantly since rock does bonus dmg to frozen targets. 
when your surrounded i like water+rock+shield and shift casting it then cold+as many arcanes u can stack and shift casted, repeat till dead. (i like freezing things) 
 
favourite beam now is steam(water+fire)+lightning+arcane since steam doesnt cancel with lightning and makes ur target wet, doubling the dmg of the beam.

For easy mob control, [shift] rock rock rock rock rock to know everything down, then [shift] Ice Ice Ice Ice Ice for a nice hefty damage.  Not great on larger beasts, but it will make the small grunts very easy to get through.

Favorites so far is anything with shield & arcane with RMB for putting down an arc of mines (frost good for slowing them down once they land). Great massive heal is the same of shield with life, repeating this will instantly heal you but also shoot up anything near the bombs (great for pushing npcs out of the way unless you want to kill them). Now if I can just figure out how to get the book on the ledge in chapter 1 (got the grease combo by rock/frost combo on the water).

" Now if I can just figure out how to get the book on the ledge in chapter 1 (got the grease combo by rock/frost combo on the water). "

(shift) lightning + arcane + ice
 
I just run around doing that and once everyone's frozen use the m60 or right click of that combination to finish em.

Arcane + Steam + Steam + Lightning + Lightning and Ice (Cold + Water) + Ice + Ice + Ice + Earth are the two best spells in the game.

Healing mine 1199 healing healing shield

I've been using SHIFT steam + lightning + arcane to clear groups of smaller guys. 
 
Ice + lightning + arcane is pretty cool too, but a bit random.

For AoE, especially earlier in the game, [Shift] 3xArcane, 2xLightning (or vice versa) should just dead any fools instantly in the immediate vicinity, without any unhealthy explosions. Pissed that I missed out on getting Meteor Storm though.

arcane x4 + shield x1 = enemy super jump pad

Press QSR as fast and spammy as you can and do the same with the right mouse button. Will kill anyone that's too close in a second.
 
Or QFQFSAA , lighting steam beam that is pretty powerful. Good if enemies come from one direction, as it's slow to aim.

SQFQFAA - arcane/steam/steam/lightning/lightning  most powerfull beam when you have a lot of enemies coming from one direction, it cleans house
FQASSS - steam/arcane/lightning/lightning + SHIFT LEFT CLICK = 3000 DMG wide area AOE , for those times when you are surrounded by assholes
FQASA - steam/arcane/lightning/arcane = THUNDERSTRIKE - 5000 dammage on 1 enemy (10k if wet) this is the hightest DPS attack period when used on single enemy, just don't use it when getting swarmed (nice boss killer)
FQASA - steam/arcane/lightning/arcane - same shit but cast it on your sword by pressing shift leftclick, your next sword swipe will do 2000-3000 dmg in an arc in front of you

Easy way to take everything down, [left] arcane, fire, fire, fire, fire. Nothing can stop it. Although i'm not very far into the game.

Another fun one that may result in killing yourself if improper combination is one that I found better than quickly casting life on yourself. Earth + life + MMB, as long as you don't overdo the earth with multiples cast at once (earth + earth + life for example) this will do a heal to you quicker, faster & more powerful (twice as much on healing last time i played it) but there is a slight aoe so if you have enemies around you it will do a slight heal on them.    
 
Also enjoying with the tree creatures on your side, instead of accidentally healing your enemies with a heal ray, just casting water on them to heal them, then you can freeze the enemies when they are farther away from the tree creatures unless you are wanting to kill them off & not needing the additional help from them.