Many animated shows, especially Japanese ones, have a habit of giving a character (sometimes more than one) an over-sized forehead. For some reason, the character, even if their head is their Berserk Button, will always take good care of their forehead, for it will always be as clean and shiny as possible. If not shinier, to the point where a common gag is to have others be literally blinded by the glare reflecting off their dome. This type of forehead could also be emphasized with the right hairstyle. Compare the less realistic My Brain Is Big.
Krillin in Dragon Ball, who actually had "Blind the enemy with the gleam off my cue ball" as one of his special attacks early on.
The Androids also have noteworthy foreheads. No wonder 18 married Krillin.
Also, one of the side effects of Super Saiyan II and III stages is a bulging forehead. Especially noticeable in stage III, where the lack of eyebrows makes it look even bigger.
Vegeta's is so notable it became a meme in Japan.
In fact, this could be said to be a trait of Akira Toriyama's art-style in general.
Yue Ayase in Mahou Sensei Negima!. One of the OAVs actually had a scene which started as if it were looking at a character through a Fish Eye Lens, only to pull back and show it was actually the reflection off Yue's forehead.
In the manga at least, characters remark on this, referring to her as "big forehead chibi" a few times. Chamo once even refers to her as the chick with the "Forehead of Doom".
It should be noted that this also falls into My Brain Is Big territory.
Setsuna's forehead is also larger than average, although not to the same degree as Yue.
This trait comes up more than a few times in fan art and doujins of Tsuruya from the Suzumiya Haruhi series.
Yukimitsu of Eyeshield 21, mostly due to him being somewhat balding.
Taiki aka Sailor Star Maker, according to the Sailor Moon fandom. This is because he/she is one of the few main characters to not have bangs.
Not commented on, but Boa Hancock of One Piece has a rather large forehead, even taking her swept to the sides hair style into account.
Vivi's forehead has also become somewhat of a meme amongst her haters. In fact, most female characters in One Piece has a large forehead, with Hancock's only being very slightly bigger than the norm and Vivi's not being bigger at all.
Sonoko Suzuki from Detective Conan , but wasn't something discussed upon.
In Petite Princess Yucie, the main heroine Yucie was often teased by Arc for her large forehead. Arc gave her the nickname "Forehead" and he often kisses it as well.
Both Masako and Himari in Mawaru-Penguindrum. Lampshaded in episode 19, where Masako confronts Himari in regards to Kanba... and their foreheads shine as they talk. It's... distracting.
In This Island Earth, the first clue that Exeter and Brack are aliens is their oversized foreheads. Mike and the 'bots do not let this pass without comment.
An early Black and White silent movie of The Strange Case of Doctor Jekyll and Mr Hyde had Hyde develope a monstrously large forehead with the hair sitting on top rather like a cap and then dangling down to emphasis the scalp. The character would wear a top hat and then slowly pull it off to reveal the ongoing forehead.
Apollo Justice in his eponymous game. In fact, Klavier Gavin, the opposing attorney, refers to him as "Herr Forehead" (Mr. Forehead). Mind you, the name started with a forehead-related piece of evidence, but it fits nonetheless.
Maggey Byrde also has a large forehead and is known as the "Goddess of Misfortune".
Blue Mary had one in Fatal Fury, due in large part to being "inspired" visually by Android 18. Her head's proportions have shifted to more reasonable levels since.
Psychonauts: Crispin Whytehead. Oh dear God, Crispin bleeding Whytehead. Not only does his forehead take up 4/5ths of his face, it seems to be flabby, hanging down over his eyes.
That's not flab, just a really heavy brow (it happens. What you see with Crispin is basically the Psychonauts version of people you'll meet who you might describe as "caveman-browed").
Victor during his headbutt special move, which grows about 3x in size.
Western Animation
Everyone in Code Lyoko. Some people even discuss who has the biggest forehead.
JFK: I can't see! Due to the glare... of Mena Suvari's enormous FOREHEAD!
Jimmy Neutron's peanut shaped head has a bountiful forehead (to hold in all that mad science, you see) with it's shape exascerbated by his large upthrusting hair cut.
Betty Boop whose design was the basis of the beginnings of the modern anime style.
Stewie Griffin from Family Guy has a large forehead to emphasis both that he is a baby and that he is sort of a mad genius plotting to take over the world. Plenty of doom involved.
Beavis And Butthead had a yin-yang take on this. One (Butt-head) had a face where the eye and nose were raised up so he had a very large head with the face splayed out over it while the other (Beavis) had his face scrunched up low down with a pronounced overbite for emphasis so that he had a lot of forehead space.
Noah from Total Drama Island, although it's more unrealistic head proportions than anything else (his hair covers most of it).
The Brain. It occasionally causes him problems, like trying to slip through a chain-link fence Pinky goes through easily.
Dib. G.I.R. hides easily behind his noggin while infiltrating an enemy base.
In Super Jail, try not noticing the size of Jared's forehead.
Ellen Page. She once joked about it by bounced a soccer ball on her forehead while on The Tonight Show with Conan O'Brien, after admitting she was extremely self-conscious of its size.
Rihanna tweeted a picture of her forehead with the caption, "New hair, new curling iron burn. Damn fivehead always in the way."
