Although liking large breasts is technically not a fetish, there's more than enough such fuel for such a kink in Girl Genius. The vast majority of female characters are, ahem, well-endowed and tend to wear clothing aimed at revealing it. Even the freaking Constructs [artificial beings] have breasts. What else? There's a considerable amount of corset play in the webcomic — the main character, Agatha, seems especially fond of them, as does her evil mother — plus plenty of warrior women and robot girls. And that's not even counting Von Pinn, the mad Construct who apparently has a thing for bondage.
Steampunk world? Check. Brainy-busty hero girl wearing *Glasses* and not much else most of the time? Mmm... Check. Lots of nummy, hyper-violent, hyper-sexed, accented monsters in uniform, complete with sexy hats? ... I'll be in my bunk.
Agatha's hair.Red strawberry-blonde, long and never gets caught in anything despite it. The above link is a fairly good example.
All this and no mention of the... umm... copious lower proportions? The author likes his females well built in general, but callipygous derrieres actually receive a bit of lampshade hanging.
Agatha's weight in general is a turn-on for this troper, who likes her women somewhat zaftig (and preferably wearing corsets).
Not a personal thing, more of a fandom observation, but a certain detail in the fourth panel of this page has caused some... interesting reactions amongst some female fans.
Ever since this troper ran into this wonderfully dark fanfic inspired by a one-off line from Othar's twitter, the Baron's infection by a slaver wasp has seemed like an awesome kind of erotic nightmare...
Speaking of Othar, tied up, heavily muscled, and a pretty decent package...the Foglios are pretty equal opportunity on this front, really...