So many of them that they were clogging up the YMMV page. Yes, like others, Magicka needs its own page.
Arcane beams, oh so very much. They have practically infinite range, fire instantly, do massive damage, cause enemies to explode when killed and damage any nearby enemies, among other things. The only downside is that they're slow to turn while firing...only you can conjure elements while you're beaming enemies to death and thus drop the current beam, take advantage of the instant cast, and blow away that enemy attempting to flank you with another beam. The result will naturally be Beam Spam.
In fact, Arcane beams were severely nerfed in duration in the PvP patch, but by equipping the Daemon's Arm Staff, you can remove the duration restriction, allowing you to fire beam spells indefinitely.
Not so powerful in PvP, as it can be deflected by casting a shield and requires you to stand still while casting.
Then there is also the M60 you get at the end of Chapter 3, if you manage to keep and maintain the weapon, you get the benefit of both high DPS, the ability to shoot through barriers and overall, the feeling of bringing a machine gun into a knife fight. Although you do have to earn it, and there can be only one, so if you lose it, it's gone for good.
Thunderbolts. Full Stop. If you're outside (and you almost always are), you can use thunderbolts. They do 5000 damage, more to iron-clad enemies, and the damage is doubled when they're wet. Furthermore, you get it really early in the game, so there's nothing stopping you from spamming it. Even the first Grimnir fight in Chapter 6 is trivial with the thunderbolt. Get him wet with a steam beam, spam QFASA, and Nullify his ghosts and shield when necessary.
Heal mines are quite effective at healing yourself and teammates, given that a single mine can heal 599 health (more or less depending on any robe attributes you may have), and an AoE cast drops twelve of them. When fighting in a group or reviving teammates, a circle of life mines can keep your allies in the fight for that much longer, or quickly get a wizard back on his feet.
Even more effective is the healing ice walls, which if done right can heal you for over 7k health. Your max health (on default robes) is 1000.
Fire/Earth AoE combo - Creates a knockdown quake that burns enemies. Using it repeatedly, you can easily stunlock enemies around you while their health is charred away.
Until the PvP patch, personal shields were pretty effective. Sure, you got knocked around a lot by physical attacks and explosions, but until they broke they completely blocked all incoming damage, and prevented you from catching fire, getting wet, freezing, and repelled beams. Not to mention, self-heal and life mines could be used to almost instantaneously restore it to full strength, or one could simply grab the life staff to gain a Halo-style shield that regenerated on its own. In the event that your shield broke, it was simply a matter of healing yourself back up, eliminating any status effects that may have accompanied the shield breaking, then simply hitting E + Mouse3 to get a full-strength shield back up.
Combining Rain and Blizzard spells slows everything (including your computer) down to a crawl. The spells themselves are easy to cast (QQF and RRQR, respectively), and their only drawbacks are that you're immobile for a few seconds while casting. But, if you can pull the two off in succession after casting a quick personal shield or successive resistances, you'll wet down everything on the screen, and then encase them in a block of ice for the next 10 seconds (not counting the thawing out or casting another Blizzard when the first runs out), making them vulnerable to easy follow-up. Enemies with water resistance will be slowed to a third of their normal speed by the Blizzard, and the ones with frost resistance are set up for easy follow-up with lightning attacks.
With the PvP patch, the Tank robes can be pretty deadly in the right situation. By itself, the Tank is pretty balanced, until you realize that it has enormous physical resistance that can shrug off projectiles... like the guns that the goblins use in the Vietnam mission.
For even more fun, there's ice and rock armor, which covers your wizard in rock/ice plates that absorb ablative damage. Your wizard moves a lot slower with armor on, but it essentially triples your life bar, only you can re-cast it at will and get another full set of armor in a single spell. And let's not even get into combining it with the Tank or Zombie robes for even more damage resistance...
The TRON robes deserve special mention as well. On the surface, it looks like a Joke Character since its Life immunity prevents you from being healed at all. But, once you look past that and see the Lightning absorption, you'll see that it means that any lightning attacks cast at you will heal you instead. This means that if you get doused (especially if a Rain spell is active), hitting Lightning causes you to heal yourself instantly without having to hit the cast button, and it turns the Useless Useful Spell Thunder Storm into a Lethal Joke Weapon, as any lightning bolts that hit you will restore you to full health while killing or knocking down enemies.
The robe in question is also weak against Arcane damage... Unless you equip Vlad's Gauntlet, giving you immunity to arcane damage, with your own life resistance cancelling the weakness to life it gives you. To sum up, this combination gives you immunity to Arcane, immunity to the otherwise-painful Life vulnerability you'd get from the gauntlet, lightning absorption...
The Rogue robe is basically this if you're a speedrunner. You're already way faster than a normal wizard, but your standard staff is a staff that teleports you backwards, allowing you to skip large parts of levels until you get the Teleport magick in Level 7. But even if you're a normal player, the Rogue's speed (especially when using Haste) and his weapon that inflicts poison (dealing damage over time and slowing down enemies) make him one of the best robes. That is, of course, if you can avoid damage because you have half the normal wizard's health.
The Space Marine robe. Period. It starts out with a very high HP limit, resistance to nearly all of the elements, and a smeggingBolt- I mean, Gyrojet Pistol which is a high-damaging ranged weapon that sets enemies on fire. The weaknesses meant to balance it (Life Immunity and Weakness to Arcane and Lightning) can be easily alleviated by using shields or (later on) grabbing the Aristo-staff (resist all, active ability teleport).