In Avas Demon, the only way to rid oneself of their demon is to do this, Inverted slightly as the demon and the living participant both have to keep their end of the bargain or they will become a 'monster of failure'.
Played straight in PK Comic when the giant fish sells his soul to resurrect Chester.
In DevilBear, the band members of Smooch (a parody of Kiss) are tricked into selling their souls in exchange for being rock stars for life. They have a What an Idiot moment, however, and Die partying too hard after their first show.
Subverted / inverted in a storyline of Fans!!: The villain, who had sold his soul to Satan for power and the chance to become a hero to humanity, manipulated Rikk into traveling to an otherworldly realm and also selling his soul to protect his friends and thus get Rikk under his power. However, the villain's plan was flawed in that he had not considered that (a) each individual person encountered the realm — and the entity within that realm — in a different way depending on who they were, and that (b) Satan was not the only celestial being interested in doing deals for souls; Rikk, being a genuinely selfless person interested only in protecting his loved ones, actually sold his soul to The Big Guy Upstairs, thus enabling him to defeat the villain.
One of the earliest strips has Riff and Torg making a deal with the devil for beer and pocket change. Luckily, the devil is short on coins.
Gwen, oh, Gwen, where do we even begin?
Riff's deal with HeretiCorp fits.
Spoofed during the Vampires arc when Torg suggests the vampires should stop sneaking around and just openly sell vampirism.
Lysinda: "Foolish Mortal... do you really think humanity would give up its immortal soul forever just to look good?" ** thinks about it** Lysinda: "Sylvia..." Sylvia: "Infomercials, next quarter, check."
Most of Chapter 56 falls into this pretty perfectly...
xkcd was all over this as a way to make fun of End-User License Agreements. 
In The Order of the Stick, Vaarsuvius tries to get one of these deals to get enough power to save his/her family. Subverted in that the powerful beings that show up to discuss the deal don't actually want V's soul's eternal damnation and act in a shocked way when V suggests that. "Oh no no no no! How would THAT be fair?" Instead, they want control of V's soul for a sharply limited time at a later point - and, not stated outright but presumed, while V's still alive. Which is arguably even worse, given the potential ramifications of having a high-level wizard directly controlled by paragons of Evil in a crucial moment. And to them, V's just a bonus. The real payoff is proving that the factions of evil can cooperate, so that they may storm the upper planes and end the war of Good vs. Evil once and for all.
"I... I must succeed". These fiends ARE trying to get V's soul; a few comics later they point out that all the evil acts that V is racking up are by V's own choice, and they are making V more "evil-aligned", away from the original true neutral.
"...but now I don't have to! Thanks, whoever did that!" You think it'd be so easy...
College Roomies from Hell!!! has the devil as a main antagonist. There are two student satanists (Steve and Waldo); it is unclear what they "sold" to obtain it, but they gain certain magical powers (or perhaps hallucinations thereof) from the devil. Eventually, Mike makes a deal with the devil to protect his loved ones at the cost of being controlled by the devil for ten minutes at an unspecified later time. Much later, this leads directly to him cheating on his fiancee to allegedly conceive the antichrist, the disintegration of his entire circle of friends, and his fatal stabbing..
While he's dead, it turns out he's apparently Michael the Archangel. Oh, great, Mike. Remembering that would have been good before you turned yourself over to the enemy.
Remember does this, with Igon's bargain with Levistus. Unusually however, we later see Levistus explaining his reasons for accepting what at first looks like a bad deal for him.
Demon Candy: Parallel starts off with TWO of these for the same character. The first is when Johnathan accidently sells his soul to Noelle for a Klondike Bar, and the second is when he makes a deal to stay in Hell with Victoria for a year to get his soul back.
Subverted in this comic of Little Worlds, where Derby insists to The Accountant that he is not making a "soul-bargain" when he demands the answers to life, the universe, and insomnia.
A major plot point in Archipelago. People who make the deal have a raven spirit enter their bodies through their left eye, turning that eye black with a red pupil. He's normally very good about fulfilling his end of the deal.
Justifed (from the demon's point of view) in Goblins. Demons feed by inflicting suffering on immortal souls, and if they can gain ownership of a soul, it can provide them with nourishment for the rest of eternity. But most of them aren't powerful enough to take souls by force; they need to persuade mortals into giving their souls up willingly.
Mentioned and subverted in Homestuck. Caliborn offers Jake English support but denies that this is a Deal With the Devil situation. Caliborn claims that Jake has nothing to offer Caliborn in return. Caliborn is merely doing this because he believes he and Jake are kindred spirits since they both have terrible social skills and because he believes Jake, being a Page, can become a Worthy Opponent.
In Sonic The Comic Online Sonic goes to the Drakon Empire and makes a deal with Master Scholar in order to try and save Mobius from Dr. Zachary and Shadow.
In Zoophobia, it's a demon's job to trick mortals into selling their souls.