This is discussion archived from a time before the current discussion method was installed.
Reverted edit from bishoujo back to shoujo. bishoujo series IMHO is too strongly identified with a guy audience, and that'd make boobs fanservice.
Dwayne Hicks: removed Sakaki from Azumanga, as I don't think she really fits the trope. She's not enormous, just a little bit more well-endowed than most of her classmates (and to a realistic degree). The one time it's used as a joke plays off the fact that she's a little embarrassed.
Shire Nomad: Would Power Girl count here, since the expansion of her chest was deliberately taken to the extreme as a joke? Or is it always Most Common Superpower when the subject is a comic book character, regardless of motive?
Sci Vo: Disclaimer: I haven't read the comic book(s) that Power Girl is in. I've read about her in discussions between comic fans of course, and my understanding was that the expansion of her chest was testing the publisher. I haven't heard of her mega mammaries being played for laughs within the work, so I don't think that it would count.
Dangermike: The "early expansion" claims about Power Girl have been extensively debunked, including by the original artist and computer analysis of her proportions in the original artwork by the too-much-free-time brigade. Myth (yes, I'll say it) Busted.
Kitsunekun:^ Just curious if you have references? Not that I doubt you, I just want to see the research (I'm hoping they have pictures :D)
Cassy: To a certain extent, Victoria Seras in Hellsing has gag boobs. She starts as very flat-chested and boyish-looking, then her breasts increase in size pretty much every time she appears in the first few episodes / chapters. In one of the omake of the manga version, Luke and his brother make fun of this (they say pretty much everything I've just written, except that they mean it as a sarcasm about the manga and its author) and conclude by saying "She has remarkable boobs... Remarkable..."
Filby: Taking out the SoulCalibur example because it's not played for laughs.
