The first thing you hear from a goblin is a call to his friend "Rakanishlol".
Also, the bleak village in the middle of the swamps in Chapter 9 features what anyone familiar with the game will instantly recognize as the Tristram music from Diablo (even though it's actually not, obviously).
Pretty much ALL of the achievement names, some of which include "I put on my robe and wizard hat" and "I think Magicka is a pretty cool guy". If it's a meme, it's in there somewhere.
The image depicting the Grease magick shows the three mages in exact same poses as the Wehrmacht soldiers from the "Hammerzeit" photo◊ (minus the leftmost one).
A sword called Stung which glows whenever enemies are nearby and the Staff of the White Wizard, which frightens enemies and upgrades your light radius.
Also the Morgul Blade, which, unsurprisingly, poisons enemies.
A wizard studying a dead moose in the first chapter mentions that "only goblin rangers are so precise".
You find two dead burned corpses in front of a burned farmhouse in the beginning of Attack of the Goblins who resemble Owen and Beru's corpses.
During the city assault portion in chapter 4, you and three NPCs will get surrounded by enemies in the town square. One of the NPCs, Admiral Agnar, shouts, "IT'S A TRAP!"
After the wizard holding the King hostage at the end of chapter 4 is defeated, he begins charging a massive lightning spell, only to have the king pick him up and throw him down a conveniently placed shaft as electricity arcs around him.
There is a lightsaber to be found next to a charred skeleton lying by a lava river...
At the very end of the game, Future Vlad, Behold the Watcher, and a hooded wizard all appear before you, like Yoda, Anakin, and Obi-Wan at the end of Return of the Jedi.
Upon entering the goblin camp in Chapter 2, the goblins yell "Intruders!" and "Blast them!"
Prior to abandoning ship in Chapter 3, Vlad says he senses a great disturbance in his town.
The Yeti from SkiFree didn't forget you; it just patiently waited until you decided to play Magicka.
Fittingly, the first time you encounter a yeti (or "Snow Troll") is at the beginning of the snow chapter. You see a soldier skiing down a snowy mountain, jumping off a rainbow-colored ramp shortly before the yeti devours him. Also, while the other trolls are very slow and the Cave Troll's instant death attack takes a long time, the Snow Troll is really fast and it devours your wizard in less than a second.
The DLC Challenge map, Marshlands, boasts the following description: Left for dead, your party must fight to survive the unrelenting hordes of the undead and all their friends."
The entire Final Frontier DLC is an obvious reference to the Star Trek series. Even the new robe is based on the Star Fleet uniform.
The live-action trailer for the new Player versus Player mode is a straight shout out to the "nicknames" scene from Reservoir Dogs.
The fifth boss, an Orcish warlord, is named Khan. The developers admit in the commentary that the sole reason for this was so the king could do a KHAAAAAAAAAN! scream.
There's a skeleton wearing brown shorts and a teal shirt lying on the floor of a tomb. Upon examining it, you're told that it "seems she was raiding this tomb".
The developer commentary/Let's Play elaborates that this reference was meant to go even further by having "milk jugs" on the floor as well.
James Bond gets an obvious reference in Chapter 4, both in dialog and in the way the boss decides to kill the king using a ridiculous contraption.
Chapter 3 gives us a twofer in the form of a stone circle with some druids and the corpse of a knight in blue. When engaged in combat, the druids shout "Shrubbery!" and "Ni!". The description for the knight says that he looks like he's had a really hard day. The sheer amount of blood and gore in the game is very much reminiscent of Moonstone as well.
The bosses of Chapter 8, the goblin ruling body, are referred to as The Aristocrats. The achievement for defeating them is called "More like The Aristocats".
One shout out doubles as a Stealth Pun - at one point you encounter a goblin archer wearing a green shirt and a hat straight out of the Errol Flynn film, making him of course Goblin Hood.
One of the bosses is introduced as Fafnir, the Burninator.
If you go into "cover mode" in the Vietnam game mode, you start to regenerate health.
Gram (of Gram's Workshop) quotes lyrics to the Iron Maiden song 'Run To The Hills' when the goblins come. "RUN TO THE HILLS! RUN FOR YOUR LIFE!"
You have the checkpoint fairy following you around, constantly interrupting with "Hey! Listen!"
Where you pick up the Nullify spell, the goblin shaman shouts Kah-lee-mah!