For lots of small enemies, I tend to use Steam + lightning + arcane 3x (QFSAAA) as an area nova. This variant of the standard "super wet lightning arcane" spell gives you a significantly larger nova while retaining the damage to splatter goblins and smaller beastmen (~2200-2000 damage). Since the third arcane is a single button, you can mash it rapidly and you dont suffer from as much slowdown.
When faced with larger hordes, I sometimes use cold tesla spires: Ice + Cold + shield + lightning + lightning (QRREAA). Be VERY careful with this one! It summons short-lived ice spikes with a sparking lightning ball on top that zaps nearby enemies for very respectable damage AND chills them - slowing them down to give you more breathing room. You can swap the cold with another lightning for additional damage if you wish: 1400~1200 with cold + 2x lit, 1800~1600 with 3x lit. It's even better if enchanted into your sword - this casts the spikes in a line that you can throw into the middle of an enemy horde, or use to engage large targets (even bosses!) from a distance. Try it against Fafnir - it will pop THROUGH his tail and hit him even while he guards!
Conflagration is definitely a favorite of mine as well - wide area, decent damage (600), fast to cast. Use it against the little daemons, goblins and enemy undead!
When panicking in close quarters, I sometimes use raw ice shotgun spam: ice/arcane or ice/lit as fast as I can hit the keys, no charging at all. I literally keep fingers spamming QRS or QRA with no rhythm and right clicking. This is very unfocused, but the sheer spell spam will deal with close targets.
Finally, the MOST powerful single target damage Ive done in the game is the spiky earth ball (Earth + 4x ice) on a FROZEN target. Get them wet, freeze them once - then cast cold + shield and put the cold wall on top to KEEP them frozen while you charge the ball. This is very useful against the yeti in Chapter 11 - total damage varies, but I've gotten over 20k with it.