In Manchester Lost, this ends up having an interesting twist. Crowley has a shoulder angel and demon represented as Inner Aziraphale and Inner Hastur. Aziraphale has an Inner Crowley and Inner Raphael. Both sets are hilarious.
In Kyon: Big Damn Hero, Achakura and Kuyou transform into these tempoarily, but neither of them quite get Black and White Morality.
Calvin and Susie have an argument in In Love and War. In responce, Spacemann Spiff and the Dictator-for-Life appear. Shortly afterwords, a Hobbes and pirate Hobbes appear as well. As it turns out, the entire shoulder angel secquence was All Just a Dream.
During the Hot Springs Episode of Tengen Toppa Gurren Solvernia, they try to talk to Kamina. The Bad Angel argues that Kamina should see the girls' side, but the Good Angel tells him to not do it, because Nia is among. Then the Bad Angel reminds that Nia shouldn't be there anymore, and thus the Good Angel tells Kamina to continue with his plan.
Played in a literal sense in Ah! Archfall!, in that Jago actually has an angel AND a devil.
In a Ranma 1/2 doujinshi (Mantou 12) Ranma's good rightious side is represented by Amelia Wil Tesla Seyruun, while his bad lustful side is represented by Lina Inverse
On chapter 3 of "Days of Futures Past What Does That Mean It Kinda Sounds Sexy" a Naruto Young Justice crossover Naruto gets excited that two of his shadow clones argue on ether doing the right thing or turning his back on the young heroes. He demands that both shadow clones transform in order to make their points first transforming into Naruko in a sexy devil costume and a white robe wearing harp player but choices to flow the good clone due to the fact the bad one snapped at him for being indecisive.
MLP Next Generation: Love Conquers All! Avarice Takes It All! has a variation: While Nidra doesn't immediately don the Orange ring that chooses her as a host, mere exposure to its Light of Avarice awakens all her darkest and most selfish impulses, which constantly battle her conscience in the form of internal dialogue.
In A.A. Pessimal's Discworld fic Hear Them Chatter On the Tide, red-haired Assassin Johanna Smith-Rhodes is caught, at a fraught time, between the Two-to-the-Power-Three Virtues and the Four-Squared-Divided-by-Two Vices. She has the Vice Anger on her right and the Virtue Fortitude on her left, both claiming her as an earthly avatar, one suggesting she go postal and use unfettered agression, the other counselling that her anger be productively channeled to bring about bloodless change. Johanna acknowledges that both have a point. Then forces the opposed qualities to clasp hands. Anger and Restraint both scream with agony as their energies cancel each other out, leavimg only an Assassin who has just won the Teatime Prize (for most inventive inhumation of a supernatural entity).
"People created you." she said. "Therefore both of you are part of me. I accept you both. But I remain human end free to choose!"
And in a chapter of Good Omens fic I shall endure..., Azaraphale points out that he and Crowley are trhe original Angel and Devil, who have been standing on the shoulders of the whole human race, ever since the Beginning...
Discord starts off with only a shoulder devil in Bride Of Discord, but Fluttershy's influence leads to him gaining an angel as well to signalize his Character Development. He also has semi-sentient reflection, who more or less serves the same purpose as the shoulder devil.
Mocked to all hell and back, in the Dan Vs. and My Little Pony: Friendship Is Magic crossover The Wheel And The Butterfly Saga where Dan only has a should devil and a slightly less evil shoulder devil (who at the time of the story, has somehow swapped places with Elise's shoulder devil, so he can torment her), while Pinkie Pie (who is currently in human form and can somehow who can see Dan's shoulder devils) has her own, which are represented by her cannon self in her regular pony form and her fannon Cup Cakes incarnation. Dan's shoulder devils are understandably creeped out and decide to get out of their.