Ned's Declassified School Survival Guide has Ned trying to decide whether to cheat on a history test — and miniature versions of Benedict Arnold and Abe Lincoln stand on his shoulders to argue the case. (Arnold's argument quickly devolves into crude jokes about how ugly Abe's hat is.) This was a result of a machine designed to put information from his history book directly into his brain blowing up.
In fact, in a later episode he talks about the machine saying something along the lines of "That thing brainwashed me. Now whenever I have a moral dilemma, Abe Lincoln and Benedict Arnold appear on my shoulders."
Herman's Head is an entire series based on this. A set of characters that represents Herman's psychological characteristics argues inside his head about, well, everything.
In Ned and Stacey, Ned's bad angel encourages him to sleep with Stacey's boss. His good angel concurs.
Subverted in episode 5 of Skins. Sid is deciding whether to skip class or not when two of his friends appear, one with horns and another with a halo◊ they stole from the drama department. After initially playing their roles, the (pill popping) angel sides with the devil and says he should skip class and get stoned with them instead.
Red Dwarf has an episode where Lister's two internal voices (his Confidence and his Paranoia) becomes actual people thanks to a mutated disease.
And Rimmer got to do the rare, full-on "all virtues vs. all vices" version on a moon where Your Mind Makes It Real.
The 30 Rock episode "Black Tie" plays with this in a rather surreal way. Pete is about to cheat on his wife when Kenneth pops in through a vent, lit by blue light, and tells him not to. Then Tracy pops through another vent, under red light, and argues with Kenneth. Finally, Pete turns to dramatically declare "I'm sorry, I can't do this — I love my wife!" You can see it here.
Neatly used in this clip from The Daily Show, in which the 'live on location' screens are gradually used to turn Samantha Bee's report on Canadian Prime Minister Stephen Harper's decision to dissolve the Canadian Parliament rather than face a vote of no-confidence into a battle between John Oliver (who is English) as the pro-Monarchy "angel" and Aasif Mandvi (who is Indian) as the pro-Independence "angel" over whether Queen Elizabeth II should remain Canada's Head Of State, with Bee the confused and indecisive Canadian trying to decide which argument to pick. Oliver wins by promising a Royal Visit.
Played for laughs in the Beetleborgs episode Buggin Out.
Blair on Gossip Girl at one point uses two of her mean girls as shoulder angel and shoulder devil when trying to decide whether or not to destroy a teacher who put her chances of getting into Yale at risk. The devil wins the argument, with the angel griping about how boring it is to play the good part.
Family Matters has this trope with Steve Urkel and Carl Winslow in one episode.
A recurring sketch on Late Night With Conan O'Brien was "Moral Dilemma" where Conan would be faced with a small one — e.g. finding a wallet full of cash and deciding whether or not to keep it or return it to its rightful owner. Suddenly, a little devil urging him to do the wrong choice would appearing on one shoulder. On the other shoulder, instead of an angel, it would be something like a bear or an astronaut, giving advice pertaining to that character.
Maybe It's Me invoked this trope as a comedic exaggeration once. Grant, a guy whose main character trait was his religious faith, had to make a decision. First, he looked to his shoulder angel, who calmly described what he should do. His shoulder devil sat sulking, and when Grant turned to him, the devil grumbled, "Why are you even looking over here? You never listen to what I say anyway."
In the Uk run of Whose Line Is It Anyway?, Ryan Stiles has to act out both angel and devil roles for 'host' Tony Slattery in Party Quirks.
Unrelated to the above, Jonathan Mangum gets the idea to do this during Freeze Tag when he sees Ryan huddled up to Wayne Brady in Drew Carey's Improv-A-Ganza. Unfortunately Ryan caught on fast but didn't act out the right role, leaving Wayne with two shoulder devils...
In a nineties episode of Neighbours, Julie Martin had the full-size versions discussing whether or not she should cheat during an exam. They weren't dressed as an angel and devil but the intention was clearly the same.
One of Babylon 5's major plot arcs was the full-on Psychomachia version of this - its creator has even described it as "the battle for the soul of Londo Mollari."
In Game of Thrones, Stannis Baratheon's main advisors are Ser Davos Seaworth (the angel) and Lady Melisandre (the demon). Where Melisandre counsels using force to achieve his goals, Ser Davos advises restraint.
An episode of Brimstone "It's a Helluva Life" has the Devil showing the protagonist all the evil he's done, to convince him he's doomed to Hell. An angel played by the same actor (but dressed like a ceiling painter as opposed to the Devi's suits) tries to convince him otherwise.
Subversions, parodies etc.
Parodied in That '70s Show episode "Roller Disco", in which Fez is tempted to take advantage of a drunken Jackie. Instead of Angel vs. Devil, he's got Batman vs. Riddler.
Subverted in the Married... with Children episode "Oldies but Young 'Uns", where Kelly's new boyfriend, Vinnie doesn't dare to touch her, because he's afraid of Al. A miniature devil and angel appear on his shoulders, and the devil says: "Oh, grab her, you've got worse beatings for less." When Vinnie turns to the angel, the angel says: "What you looking at me for? If I wasn't so tiny, I would be wild-thinging her myself!"
How I Met Your Mother: At a Halloween party Barney (dressed as a devil) and another guest (dressed as an angel) argue about whether Ted should urinate from the roof... at least until the angel asks Ted and Barney for marijuana.
Made more amusing when Barney tells the other guest to "Go to Hell."
The Fresh Prince of Bel-Air gives Will two devils. While he's deciding on whether to "borrow" the car keys and sneak out, his shoulder devil appears. After the devil tells him to take the keys Will expectantly turns towards his other shoulder, only to have his other shoulder devil appear and tell him to take the damn keys already.
A similar example from the 2011 series of Rab C. Nesbitt. While trying to resist the demon drink, a devil appears on Rab's shoulder in the form of his mate Jamesie Cotter. Rab is Genre Savvy enough to know that he should wait for his good angel to appear (and tells the audience as much). The second angel duly appears in the form of Shane MacGowan, telling him "No luck mate, you've got two bad angels."