Actually, as with the Wicked Witch, an evil laugh is also traditional for a Mad Scientist character (though not all of them).
In Baldur's Gate, Sarevok from the first game is available in the final expansion as an optional party member. His maniacal laughter is one of his battlecries and he'll sometime throw his evil laugh when you give him orders.
Gruntilda in Banjo-Kazooie. She gave out a rather impressive evil cackle whenever you hit the "Save and Quit" option in the menu.
During her introduction as a real-life Alice Angel, there's a part between her Jump Scare and the lights coming back on where she laughs.
At the end of Chapter 3, as the elevator is ascending, she's monologing about heaven. She tells Henry that she thinks she'll never get to see it and starts sobbing. However, her sobs quickly turn into evil laughter and she reveals that she had no intention of letting Henry and Boris escape because she wants Boris's insides. Then she causes the elevator to plummet with those two on it.
In BioShock, Atlas/Frank Fontaine bursts into an Evil Laugh once you have killed Andrew Ryan and shut off the self-destruct. Arguably, this is also a moment of Nice Job Breaking It, Hero!, although one built into the game's plot.
In what is probably the strangest example ever seen, the vending machines have a truly unsettling evil laugh.
Wait till you see the one in Hephestus that is broken and lobs grenades at you.
Any appearance of Big Bad Dr. Goldfire in the Blake Stone series is accompanied by his trademark "BWAHAHAHAHAHAHAA!"
Terumi Yuuki from BlazBlue, befitting of his Troll archetype, enjoys his Evil Laugh all the time, especially when mocking his prey's miseries.
Rukifellth: Once I regain my earthly body, I shall create a new cosmos. MY Cosmos. A cosmos of chaos where only the strong shall survive! Ha ha... Ha ha... Bwah ha ha ha ha ha! (5 second pause) It's not much fun making speeches about my plans without an audience...(pause) Ha ha...Ha ha...Bwah ha ha ha ha ha!
Castlevania's version of Dracula loves doing this, and since he's voiced by Norio Wakamoto, it makes it all the more enjoyable. It's also apparently a mandatory thing for the Lord of Darkness, because Soma Cruz does it, too.
Castlevania: Curse of Darkness has Isaac, who has an amazing crazy laugh in both the Japanese and English voice tracks. The one in battle is bad enough (because he's about to kablam you across the arena with a certain attack), but in a particular cutscene (when Dracula brainjacks him and shanks Trevor Belmont), it's just - yeah. Don't play the game in a dark room when you approach that point. Isaac's English voice actor is, incidentally, Liam 'Also Lezard Valeth' O'Brien.
Dracula has a wicked snarly cackle in that game too.
Barlowe's laugh, especially when he frees Dracula's soul.
Patrick Stewart, playing as the Necromancer, did a rather hilarious evil laugh in Castlevania: Lords of Shadow, probably due to his not being accustomed to playing a bad guy.
The Cat in the Hat: Mr. Quinn occasionally exercises his evil laughter during his speaking parts.
In Cauldron 2 for the Commodore 64, the witches have a good, hearty, and, by today's standards, painfully artificial sounding laugh each time the player dies. And it happens quite a lot, this being a Nintendo Hard game.
In Chrono Trigger, if you choose to sit down on the evil-looking throne in the Giant's Claw, really the Tyranno Lair long after Azala's defeat, the character in the front of the party does an Evil Laugh.
Wannabe mad scientist Vernon Von Grun frequently does this in City of Villains when you report back to him after a mission. It is made funnier by him asking you if you can tell that he's been working on the laugh, the laugh changing a few times, him asking you to join him in the laugh, and once breaking into a cough mid-laugh.
There is also an evil laugh emote for the players; though it lacks sound, it does go through physical motions that would make Doctor Frankenstein proud.
The evil AI CABAL in the Command & Conquer: Tiberian Sun expansion pack Firestorm will, occasionally, do the mechanized Evil Laugh in the middle of a mission to taunt you.
Kane himself indulges in this trope during the intro to the GDI campaign of Tiberian Sun. Being the Magnificent Bastard that he is, however, his laugh is a confident chuckle instead of a crazed cackle.
Tanya from the Red Alert series likes doing this a lot, and, in at least one promotion video of Red Alert 3, Emperor Yoshiro and Premier Anatoly Cherdenko do this together with Tanya.
Lampshaded in The Curse of Monkey Island. During Guybrush's first encounter with Murray, the Demonic Talking Skull, Murray busts out a laugh and Guybrush asks him about it. Murray (whom Guybrush had just blown apart) says that there's a fish nibbling on his foot somewhere and it really tickles.
Above lampshading happens in the first few minutes of the game. The trope is played straight in the rest of the game. He really likes to let us know who he is.
Murray: I AM MURRAY, THE EVIL DEMONIC SKULL! BWAHAHAHAHAHAHA!
King Andre, the smuggler leader of Skull Island, has a fairly impressive evil cackle that he breaks into for no apparent reason. Guybrush eventually asks him to stop, as it's fairly unnerving.
In the first game, Gengar has his well known, "Keh keh keh!"
Jedah of Darkstalkers is normally unflappable and very polite, but occasionally will indulge in a bit of mad laughter; most notably in one of his supers when he drags you underground and has hands of blood beat the crap out of you, or during one of his victory poses while gouging his eyes out!
In Dark Souls, Lautrec ends all of his dialogue with an Evil Laugh. It's not surprising that he turns out to be one of the few truly evil characters in the game.
"Trusty" Patches has an assortment of evil laughs, ranging from a suspiciously evil chuckle, to a full-blown diabolical laugh once he kicks you into a pit.
It comes to the point that whenever Laharl shows up in the sequels, the first indication you have that he has appeared is his (very recognizable) Evil Laugh piercing the air.
Badly attempted by evil clones of Kurtis in the sequel, Disgaea 2. Given the fact that their speech is more stilted than William Shatner, it comes out as a robotic "HA hee HA HA."
Like Laharl, Mao, the main character of Disgaea 3, will actually begin his respective turn with a humorously quick but evil "Mwuhu-haha!" What make it funnier is hearing it from the same voice actor that does Edward Elric in the English dub of Fullmetal Alchemist, Vic Mignogna. In the Japanese, it's loud but simple "HA HA HA!"
In Disgaea Infinite, Laharl and Mao try to brag about themselves while punctuating it with their Signature Laugh. As the exchange continues, both of them drop the bragging and just straight up try to out-laugh each other. By the end, the two are clearly straining themselves to get another laugh out despite having lost a lot of air and straining their throat in the process.
Appropriate for one seeking to be a final boss, Desco of Disgaea 4 uses a short, simple "Fuhahaha!". The evil factor of it is watered down a bit by her cutesy voice, though. There's also Valvatorez, who uses a calm "Hm hm hm..."
Few have a more evil and constantly used laugh than Overlord Zetta, he will even laugh like a maniac during his signature Zetta Beam attack.
Honestly, anyone with a good enough title will be subject to this trope, especially the Overlords in the Disgaea series and Makai Kingdom.
In Donkey Kong 64, this is done by both the Big Bad King K. Rool and the insanely creepy third boss Mad Jack (who's laughter is part of the background music).
Oddly enough, it's also done by Bleak in Donkey Kong Country 3, when he's hit by one of the Kong's attacks.
Although he's pretty completely Lawful Good, Alistair of Dragon Age: Originscan do an impressive Evil Laugh anyway. (Unless he spoils it by coughing in the middle, as he does once.)
Played much straighter, some of the darkspawn have extremely deep, growling, guttural laughs.
The Mother does this at the tail end of her first cutscene in Awakening. It's definitely Fan Disservice and intentional horror because her bare breasts jiggle while she does it. All eight of them.
During the ending of Marooned the villain Radimar had an evil laugh which lasted so long and had such an overabundance of reverberation at the end that it quickly descended into Narm territory.
Dwarf Fortress: Dwarves will "loose a roaring laughter, fell and terrible" when they enter a Fell Mood, during which they will murder another dwarf and use their corpse to make an artifact.
Dynasty Warriors and Samurai Warriors both feature some characters sporting some pretty evil laughs. While one could probably credit Oda Nobunaga with a pretty cold chuckle, it's Sima Yi of Wei who takes the cake, with a gleefully wicked laugh from practically every person who's voiced him. Probably achieves its height in Dynasty Warriors 5's Expansion Pack, where he cackles loudly and dismissively at an enemy general's corpse in a cutscene, and several of his moves are punctuated by evil laughter and constant use of the word 'fool.'
Kefka of Final Fantasy VI had a grand evil laugh of his own, instantly identifiable by anyone who's heard it. This is especially impressive as the game has no vocal tracks. In fact, his evil laugh was so well-known that he actually named one of the subtropes for an evil laugh: Laughing Mad. Note that Kefka has also been added under the entry for Un-Evil Laugh, showing that sometimes this can be YMMV.
In Dissidia Final Fantasy, he gets to laugh at the heroes together with Exdeath from Final Fantasy V during the opening of Shade Impulse. Kefka's high-pitched howling and Exdeath's deep belly laughter mix together well.
In Fire Emblem: Three Houses, Hubert, who's evilness is debateable though even his allies think he's pretty sinister, has a wide range of evil laughs. Sometimes it's low and sinister but other times it's hilariously over the top. It's hinted that he might be doing this on purpose.
In Fist of the North Star: Ken's Rage, quite a few characters possess evil laughs, which is not unheard of for the series. However, what is notable is that Souther/Thouzer not only has a spectacular evil laugh which can be activated at will, but that it's also weaponized. Tapping the special move button makes him cross his arms in a Badass Arm-Fold and laugh evilly, while spontaneously making everyone within about ten feet of him explode into bloody chunks without actively touching them.
The final boss of Gradius Gaiden is the only one in the series to possess one. He laughs at the player while taunting him, though he's as powerless as every other final boss.
Grandia II's Melfice loves to laugh evilly. So much so that in battles with him, he never actually stops laughing.
Father Grigori in Half-Life 2 is not evil, just crazy, but laughs evilly anyway as he shoots zombies.
From Halo, there is but one maniacal laugh, but considering who it comes from, it's creepy. Y'know how, villainous as he was, the Flood Gravemind always seemed fairly calm and convincingly sane for a monster in any previous talks or encounters? Well, all of that is thrown away right after the final obstacle to his plan dies in Halo 3, and he lets rip a spectacular one. It's even worse when you remember (and hear) that even his voice is composite in nature. Listen to it here, and crank up the volume after the 'obstacle' dies.
He has a knack for doing this when his victory is (supposedly) assured. The Librarian mentions in the Halo 3 terminals that at the climactic final point in the Forerunners' war against the Flood, the Flood were... flooding every channel they could find with laughter. Imagine... trillions and trillions of assimilated aliens of countless species all laughing with the distorted, horrific voice of the Flood.
Leopold Charles Anthony Weasleby the Third from Henry Hatsworth in the Puzzling Adventure is unique in the fact that his Simlish Speak is mostly compromised of variation of his maniacal cackle and sneer. Cole actually has a similar one, which is not surprising since Weasleby is actually a robot that Cole created to antagonize Henry.
Dr. Curien, the staple Mad Scientist villain from the House of the Dead series, gets a rather memorable one in the third instalment. As the mid-chapter cutscenes up until that point had depicted him as a benevolent scientist seeking a desperate cure for his son's illness, once he lets the laughter loose, you know he's gone bonkers.
Iggy's Reckin' Balls has both Narlie and Skully. Narlie's laugh is a very deep "Huh huh huh huh...", while Skully's is a high-pitched, fast cackle.
The Commodore 64 port of the 1984 computer game Impossible Mission is one of the earliest examples of digitized speech in a game. The villain's evil laugh signified that the clock had run out and the game was over. (Conversely, if the player successfully completed the game, he gave a kind of Big "NO!".)
Xemnas also has a good one (kind of requisite for any villain voiced by Norio Wakamoto), though in Kingdom Hearts II, it's mostly drowned out by the sound of the Beam Spam he's unleashing when he does it. You can hear it much more clearly in Dream Drop Distance while he's chucking buildings at you, though he doesn't always decide to use it.
When the surviving Organization members first appear to Sora & Co., they have a chorus of evil laughter at his expense. Most are pretty good... and then there's Demyx's rather unintimidating giggle.
One of Iori Yagami's more beloved traits in The King of Fighters series is his habit of breaking into maniacal laughter when he wins a match. This is a bit odd, considering he's also a protagonist. Sample (the AMV Hell project mixed this with footage of Light Yagami, whose name is pronounced the same way).
Iori with Flames also laughs maniacally in KOF XIII whenever he completes his Shiki Saika combo, his Neomax also has him briefly enter the Riot of Blood state whereupon he laughs evilly and then crushes his enemy with a massive ball of flame.
Ryuji Yamazaki has a really crazy laugh that's heard in his winpose (example). 2002 Rugal has a good one, too, but it's to be expected since it's Norio Wakamoto. His original voice actor, Toshimitsu Arai, pulled off a pretty great one in '98.
In Kirby: Planet Robobot, President Haltmann arguably pulls this off better then any Kirby villain to date, starting with a subdued laugh at the beginning of each phase of the fight, and letting out an amazing one when he unleashes his ultimate attack.
The Legend of Zelda: Ganondorf has his fair share of laughs. Sometimes, it is a simple, self-satisfied "Hm-hm-hmm...", other times, it is used in a mocking tone after he has succeeded in an attack.
One of the most flamboyant is in The Legend of Zelda: The Wind Waker where, after the King of Hyrule uses the Triforce to wish for "hope" for Link and Zelda and the old Hyrule begins to flood and vanish under the water, Ganon starts to laugh madly, his sanity broken at seeing all his dreams smashed before his eyes. The laughter continues to grow until he is eventually practically shrieking. Some found it quite silly, others thought it was pretty awesome.
To say nothing of what he was like in Zelda II: The Adventure of Link. When you get a Game Over, the evil Ganon laughs at you with the caption GAME OVER RETURN OF GANON. Subverted in the FDS version, where Ganon gives some kind of roar (or a glitchy electronic sound on a poor emulator).
You can hear the same laugh in Ocarina of Time, but it doesn't quite have the same context...
Then there's his laugh in Super Smash Bros. Brawl. Specifically, in Subspace Emmisary. He's laughing from across a very shaky holographic interface, so his laugh dissolves into the most malevolent sounding static you've ever heard in your life.
In Blue's Journey for the Neo Geo, the Daruma Tribe's invasion in the introduction is followed by the Daruma Emperor popping up to say "GAHAHAHAHAHAHA."
Klogg, the villain from The Neverhood, has a pretty awesome laugh, which not only appears in the Bad Ending (which manages to top it by having the hero, Klaymen, do an even better one of his own, after his mutation into a Klogg-like being), but in the opening credits as well.
Wheatley in Portal 2 gets one, which seals his FaceHeel Turn, and later comments on how exhausting that kind of laughter is.
The defective turret you designate as the new master turret template will emit one whenever one of its faulty brethren makes it past quality control or when one of the functional turrets gets launched into the incinerator.
Although he mostly avoids this in all his other appearances, Albert Wesker can't resist letting fly with this in Resident Evil Code: Veronica. He's definitely outclassed by the Ashford twins, though; both seem to have a rather serious, nay, terminal case of the sillies.
There's also Marvel vs. Capcom 3 where he does it with his moves like shooting his opponent with his Samurai Edge.
The Prince in the early parts of Rule of Rose has an Evil Laugh that varies from quick giggle to truly psychotic cackle as he has Jennifer in his power. He becomese much more subdued later on, however, as his role in the story becomes more ambigious.
The Prince: For I am the Prince, and the Prince rules! Mwahahahahaaa! This is your life, but you're playing by my rules! Hahahahahaaa!
In Persona 5, the anti-heroic protagonist's starting Persona has an absolutely diabolical laugh when he's summoned for the first time.
Walter Sullivan from Silent Hill 4 laughs before, during, and after he attacks you, as well as when you are attacking him.
Evil Witch/Warlock Sims in The Sims 2 had idle sequences in which they would cackle and perform Finger-Tenting. In Sims the Third, if your character has the Evil trait, they'll cackle and wring their hands in the most satisfying way, point ominously at other Sims and gloat about...their impending doom?
Alistair: AAAAAHAHAHAHAHAH!!! AAAHAHAA- *cough, choke, gag* I swallowed my mint.
Luca Blight from Suikoden II had an evil laugh accompanied by an enormous amount of exclamation marks.
In Sundered, the boss Dominion greets the player with a malevolent chuckle before putting on his mask and starting the boss fight. The Shining Trapezohedron also indulges in maniacal cackling on occasion, most notably during the final boss fights.
Paper Mario: The Thousand-Year Door has five villains with their own distinct laughs. Emperor Grodus' is something like "Gaaack aaack aaack aaack aaack"; Lord Crump' is a "Buh! Buh huh huh huh huh!"; and Beldam's is "Mwee hee hee hee hee".
Also, Doopliss's "yuk yuk yuk".
And the Shadow Queen's "Muh huh huh huh huh".
Being who he is, Wario has been known to do this. He even does this in his first appearance (Super Mario Land 2), or at least that's what it's supposed to sound like.
WAH HA HA HA! AHH HAH HAH HAH!! WAH HAH HAH HAH HAH!!!! One of his victory taunts in Super Smash Bros. Brawl. Very nice, Wario.
Tekken Bryan Fury in has a particularly disturbing one, thanks to the mechanical effect on his voice (due to his being a cyborg) but the iconic laughter was changed in Tekken 6, much to the dissapointment of the fans.
Then there's Devil Jin, who has a Jokeresquely high evil laugh after winning in a fight, complete with an evil grin, showing off his pearly white
In Tekken 5, Jinpachi Mishima, The final boss and Kazuya's grandfather has been possessed by a demon and comes with a demonic voice and his intro pose shows him doing an evil demonic laugh, he also laughs demoniacally when he manages to hit the opponent with his fireballs
In the Street Fighter series, Sagat was the first to break out the evil laugh whenever he wins a match, which he still does to this day.
Juri Han has a real evil laugh whenever she wins a match.
Oni laughs if his Meido Gohado knocks you out in Street Fighter 4: Arcade Edition.
Subverted with Chun-Li, as her laughter is not evil.
Wild Dog laughs in every appearance in the Time Crisis games.
The Guardian from the final Ultima trilogy had a particularly memorable, bass-pitched, resonating laugh, courtesy of Bill Johnson and a filter that made his voice progressively deeper in each of the games.
Flowey of Undertale has a creepy laugh that he pulls out often against you. The Fallen Child has an even worse one.
When being hacked in Welcome to the Game, you're presented with a digital skull avatar who gives a flat, robotic laugh.
Elisabeth from Witches' Legacy has a pretty awesome cackle in the style of the Wicked Witch of the West.
In The Witch's House, reading a story about how a man killed his dog over a misunderstanding causes a creepy laugh to reverberate throughout the room Viola is in. It's most likely Viola/Ellen herself laughing at the story.
Also, blood elves, to some degree; the females especially sound rather psychotic. The male gnome and (ironically) draenei /laugh emotes (respectively a high-pitched cackle and a raucous guffaw) also sound a bit maniacal. And female trolls sound like the Wicked Witch of the West.
Due to the introduction of death knights, every race and gender can now have one, via an optional sound filter.
Many, many bosses in WoW invoke this trope.
Malygos: What could you hope to accomplish, to storm brazenly into MY domain? To employ MAGIC? Against ME? BWAHAHAHAHAHAHAHAHAHA!
Sellers, the resident Mad Scientist, does one when Jr. and the others find out that Dmitri, Jr.'s crazy father, is going after the Durandal and its crew. It's not nearly as maniacal as Albedo's is, but it's still worth mentioning.
Also, the Patriach has a paticularly weird one.
XCOM: Enemy Unknown: Your psionic troopers give bloodcurdling ones when they use Mindfray. It either makes you chuckle along with them or makes you wonder if Dr. Shen was right...
Mojo does this in X-Men (1993) any time you him if you don't strike his vulnerable place.
Mojo laughs every time you hit him in X-Men (1993) unless you manage to strike his vulnerable spot.
In Yandere Simulator, the laugh button can be pressed three times in quick succession, graduating Yandere-chan's innocent giggle to cackling like a madwoman. Evil laughter can actually help restore your Sanity Meter. Just be careful that your fellow students don't see you laughing like a cartoon villain, lest they think you a nut and cause damage to your reputation (or worse still, if Senpai sees you...!).
In Ys II, Dalles generally uses his sinister laugh to announce his presence.