Used in Dungeons & Dragons, where demons and devils can be summoned, and make pacts with mortals. Notable in that they CAN, in fact, grab your soul and run if you mess up the pentagram, and if you forget 'Promise not to kill me when you're done' in the contract, you are in trouble.
There's also a demon named Pazuzu who gives a wish in exchange for going one step closer to Chaotic Evil on the alignment chart.
The book "Fiendish Codex 2: Lords of the Nine Hells" actually deals a lot with how devils do those Faustian deals. Devils have rules they must follow for contracts (they can't directly force someone into making a deal, for example) and hell even has its own appeal court run by a pit fiend for souls who believe their contracts were not fulfilled lawfully. And yes, while very hard-assed (you better know infernal law real well to win there), said court actually works, meaning that if you are right and can plead better than the devil who made a deal with you, you can win your soul back. Because devils get your soul if you are Lawful Evil when you die, not all contracts require your soul as payment; quite a few contracts will simply require the mortal to do a series of actions that will eventually make him Lawful Evil. This method has the advantage of not giving the mortal a chance to go to court for his soul once in hell (since he's there not because of the deal, but because of his alignment).
Fiendish Codex: Of course, even if a mortal does manage to win his soul back legally, it is quite possible for him to still end up in Hell by dint of his alignment. Much diabolical laughter ensues.
To be specific, the 4e warlock gets its powers from one of the following pacts; the dark pact, with demons; the fey pact, with creatures of the feywild; the infernal pact, with devils; the star pact, with creatures of the far realm; the vestige pact, with various remnants of dead powers; the dark pact, with horrible things from beneath the earth; the sorceror king pact, from the horribly environmentally destructive uber-mages of Athas, and the Gloom Pact, from what is essentially the Dark Powers or the Darklords of Ravenloft given a new backstory. These forces are generally evil, or at best extremely alien, but what prevents someone from automatically becoming evil from making these pacts is that they can actively work against their patrons, even with that power.
Binders, meanwhile, are accused of this, but since the vestiges they form pacts with do not give a toss about what people do with their power beyond a few weird behavioural restrictions, they end up as a subversion - sometimes forming a pact with a being from outside existence for power just works.
A variation occurs in Mage: The Awakening, with the beings known as the acamoth. The acamoth make deals with mages (and possibly other mortals) whereby they consent to allow the acamoth to enter their souls and Mind Rape them. If the mage survives with their sanity reasonably intact, the acamoth are obliged to grant them powers. The acamoth are noted to not have much interest in souls which are already corrupt, and are generally concerned with inscrutable, long-term goals (ie, conquering reality), which means they will rarely take a soul outright (a comparison is made to financial investment).
Also toyed with in Changeling: The Lost. A Changeling or True Fae can bind a human to a Pledge, offering money, power, or other benefits in exchange for various favors - but most Changelings, due to the importance of contracts and pledges among the fae, are geniuses at twisting the meanings behind the words of their pledges. Not only that, but an agreement with the True Fae has a better-than-average chance of ending in the human kidnapped and subjected to Mind Rape in the True Fae's Arcadian realm. Best case scenario: he escapes as a Changeling. Worst case? You don't want to know.
Hunter: The Vigil and World of Darkness: Inferno also include rules for making dark contracts with demons; some of these are the traditional "sell your soul" variety, while other simply require you to perform actions that feed the demon's Vice. Many of these demons are actually remarkably straightforward in their dealings, and that hunters often find themselves searching for loopholes and hidden clauses that aren't really there.
Mage has lots of other examples, including the Lethean (offers to take away painful memories or things you'd rather not percieve, the cost is that you're giving up parts of your memories and perceptions), the Oath of Ruin (offered one guy Awakening in exchange for coming through once he had enough living descendants, and is outright stated to only be banishable by doing something truly evil), and the Scelesti (mages who twisted their souls in exchange for power).
It shouldn't be a surprise that Demon: The Descent has these, and a nasty variant. Demons effectively make soul pacts with mortals, offering things in returns for aspects of the mortal's existence. These aspects are then used by demons to cement the Covers that keep them hidden from the agents of the God-Machine. A number of demons go for a kind of pact that's only cashed in if the demon's Cover is destroyed entirely... but if that happens, the demon can just adopt his thrall's existence instead. And the thrall vanishes. Utterly.
The most traditional variation is seen in Demon The Fallen, in which a Fallen character can make a mortal human their "Thrall". In exchange for the usual stuff like health, luck, romance, etc., the human becomes permanently bound to the Demon and has to fulfill their part of the deal in addition to supplying their master with Faith (used to cast magic). Thralls do have free will and can contemplate a Faustian Rebellion but the only way to break the connection is actually killing their master, which is not exactly simple. Additionally, there are the Earthbound, who Mind Rape their Thralls to make them completely obedient slaves (who cannot provide them with Faith, though).
The Vampire: The Masquerade supplement Guide to the Sabbat had rules for Dark Thaumaturgy, which is Thaumaturgy taught by demons, frequently involving a Faustian pact. Aside from the hatred and fear with which many infernalists (as Dark Thaumaturges were called) were viewed (especially the Sabbat, who are very big on not being under another being's thrall), the rules even specifically stated that the Storyteller now could have the character dragged straight to Hell at any given time, like, say, if they felt the character became TOO powerful.
The Chaos Gods of Warhammer and Warhammer 40,000 often empower their mortal followers: Khorne can bestow martial prowess and brute strength, Tzeentch can grant a worshipper sorcerous power or fate-weaving cunning, Slaanesh boosts a person's charisma and makes their senses keener, and Nurgle's followers have their lifespans increased and become significantly tougher. In rare cases, these pacts work out. More commonly, Chaos worshippers fall prey to the very pacts they made: Khorne's followers become mindless killers consumed by bloodlust, spilling their own if no foes present themselves. Tzeentch's devotees end up power-hungry, paranoid, and trapped by the complexities of their scheming, or even betrayed by their patron as part of the god's Gambit Roulette. Slaanesh's disciples become addicted to sensation of any kind, be it mind-rotting drugs or self-mutilation. And Nurgle's cultists are turned into festering, putrid husks, whose corrupt bodies are so tough because they're rotted past the point of feeling pain anymore.
In any case, the road of a champion of Chaos only has two destinations: ascension to a full-fledged daemon prince, or else all the gifts and mutations cause the aspirant's mind and body to collapse into a bestial chaos spawn.
The best part is since these are gods of chaos, making a pact with them in the first place can be difficult - they're just as likely to notice and reward some dabbling nobleman than a warrior who battled for decades in their name.
You can make these pacts in the Dark Heresy RPG, though it may be hard to keep them concealed from your teammates...
A really bad Faust comes from the Warhammer spin-off Mordheim. Nicodemus asked a Greater Daemon of Tzeentch to become "the greatest wizard of the Old World." Wish granted. He discovered an antidote before he grew too large, but he requires a constant supply of Warpstone to manufacture it.
Mutants And Master Minds has one in the form of Mr. Infamy, who looking to make this kind of deal. It doesn't matter if it's a normal Joe, a superhero or a supervillain.
Exalted has a number of versions, seeing as tacitly summoning and bartering with demons isn't exactly frowned on by the religion of the Realm, but the most traditional might be Abyssal Exaltation. One of the Deathlords comes to you on your deathbed and promises you a second chance at life, as well as power beyond your imagining... as long as you'll bind yourself to his service, throw your name into the Void, and aid him in the destruction of Creation.
And then there are the more traditional devils, the Yozis. One of the ways the Yozis recruit the Green Sun Princes is to go to a mortal who had a chance of performing great deeds that would have lined them up for Exaltation, but backed down in the face of adversity. The Yozis then offer them a second chance at greatness...
And then there are the akuma, Exalts and "enlightened" mortals who threw their lot in with the Yozis. The resultant procedure gives them great power, rapes their free will out of existence, and turns them into a very intelligent oven mitt with a daiklave. Yeah, becoming akuma is rarely a good idea.
Among the Green Sun Princes, the favored of Cecelyne can make these and dictate terms thanks to the Verdant Emptiness Endowment Charm, which allows them to answer wishes made even in jest. Further Charms allow them to grant further benedictions and heal the grievously wounded... as well as revoke their blessings, painfully, if payment isn't offered up.
The fan-made "Terrifying Argent Witch" remake of the Lunars enables them to play the part of the Devil; fulfilling a spoken desire (serious or not) in order to "buy" someone's shape (and possibly soul, given how Lunar shapeshifting works), sealing oaths in blood (complete with a terrible curse should they break the pact), lending power at the cost of being emotionally tied to the Witch in question.
This is a large part of Black Magic in Magic: The Gathering. The most up-front about it are the demons you can summon, especially the flavour text on the latest reprint of the classic Lord of the Pit: "My summoning begins your debt, planeswalker". The character Liliana Vess has a major deal with dark forces in her backstory.
Quite common in Deadlands. Nearly all magic comes from the spirits of The Hunting Grounds. The nice ones are in the minority. The most common playable version of this is The Huckster, who has to allow a demon into his body in order to cast a spell. Just hope the Huckster isn't tricked into giving the demon too much control.
Played straight and toyed with in Nobilis. The Cammorae play both sides. They're Faust when they make a deal for whatever powers they receive and lose their humanity. They fit in the Mephistopholes role when the player characters contract them to do something. First and second edition Powers of Hell also play with this trope. Many love buying souls, with the full knowledge that such deals don't actually do anything. Humans that think they have no soul have no reason to act virtuously, and will probably become corrupt and hellbound in the process.
In the Yu-Gi-Oh! game there is a Spell Card called "A Deal With Dark Ruler" where the card art suggests this, showing a man making a deal with Dark Ruler Ha Des, a powerful Fiend-Type Monster in the game. (The card's actual effect has nothing to do with Dark Ruler Ha Des or Fiends; it lets you summon a powerful Nomi monster called Berserk Dragon if one of your a Level 8 or higher monsters is sent to the Graveyard during the turn it is activated.)
In The Dark Eye there are twelve Demon Lords as well as several powerful so called free demons one could forge a pact with to gain gain access to special powers depending on the lord and being able to summon his or her servants more easily. The downside, aside from eventually going to the hells, is that over time anyone with a pact will start developing character traits that fit those of his demonic liege. So a person with a pact with the Lord of Strife and Movement will develop a Chronic Backstabbing Disorder and soon won't be able to stand still or even sleep anymore, while someone with a pact with the Lord of Slaughter and Bloodshed will become more vicious in battle and start developing wounds that always bleed but do not weaken him.