There's a Good Angel, Bad Angel scene in its first episode which culminates in "Good Excel" blowing away "Bad Excel" with a huge pistol ("The bullet of Justice caps Evil's ass!"). Good Excel later gets hauled off by teeny-tiny little Police Excel for murder, while Excel herself is confused and strangely philosophical.
Played straight but still very oddly in the manga: Watanabe is debating whether or not to give Hyatt CPR, and is so torn over his intentions that a battle erupts in his mind between Hypocrite Watanabe (dressed like an angel but actually the one representing his perverse side) and Bancho Watanabe (who's dressed as Jotaro Kujo from Jojos Bizarre Adventure).
Chiaki and Fujioka both have an angel and a devil appear behind them in the second episode of Minami-ke Okaeri.
Rahzel: Tons of little Rahzels are having a wild party in my brain.
The female protagonist of Hana Yori Dango had a good angel telling her not to marry a rich Jerkass and a bad angel telling her otherwise.
There's a scene in NEEDLESS where Blade tries to hit on a currently-crossdressing Cruz, only for Cruz to remind him he's a boy. Blade's angel and devil appear, and both tell him that gender doesn't matter, as long as he's cute.
In one of episodes of the DVD series Growing Up With Hello Kitty, Hello Kitty has trouble with patience and has to deal with this several times. Each time the devil wins, he does a Happy Dance. Eventually, the angel wins, but the devil is a sore loser. He shows up several more times, each time looking more battered and beaten and at the end vows to find a new impatient kid to pester.
Yandere Kanojo: Reina met them in the chapter where she tried to find out the reason Manabu wears glasses without need.
Cooking Papa: Araiwa's look and dress the same way (business suit) and only by their advices we can tell who's the good one and who's the bad one.
The gag manga Cut Away has a girl find a wallet. Immediately her inner angel and demon start arguing over what to do... soon joined by her inner Buddha and inner Shiva. Eventually all manner of inner mythological being joins in the debate ("And they all have my face!"), only to be silenced by her inner high-school principal.
Friend: So what happened? Girl: They all went to their class reunion.
Hinagiku gets her own versions late in the manga as well while she is sick in bed. Her angel self thinks she should just go to sleep to get better quickly, while her devil self thinks she should let Hayate (who's taking care of her) spoil her a bit. Hina covers devil!Hina in an empty cup and rolls over in her futon. Angel!Hina is proud of her...and then Hina calls to Hayate to ask for a peeled apple cut like rabbits. Her angel is upset but Hina argues that she is going to sleep, after letting Hayate spoil her for a bit.
They're not on her shoulders (one appears in front of her to stop her and the other is sitting on her head), but this happens to Kyoko in Black Cat. They both have her face, and the angel's dress has "kind" on the front where the devil's dress has "wicked." When Kyoko makes the right decision, the angel is seen punting the devil.