I'd have to vote Saori from "Mahoromatic" (the 25 year old perverted teacher) as her perverted aspect makes up for the fact that she's only slightly bustier than Nanako. I mean she's kind of like Misato from "Evangelion" if she had been a teacher and her childish and ped*philiac tendancies took hold of her main personality. Also, keep in mind that she dons a swimsuit that pretty much only has verticle strips of cloth that cover her nipples, then stretches downward and comes together to cover her crotch. Oh and there tends to be the running gag of the title character's being quite small compared to this instructor's hefty bosom (at one point, 2nd season episode 3, the episode is all about bust size and a bust enhancing machine gets a little out of control for some temporary B.E.)
I'm surprised that Saori wasn't mentioned here as this series has been mentioned quite a bit on this board.
--On a side note, watch a few other Gainax series like "Gunbuster" where the enemy has organic looking attack craft much like the 'enemy' in "Mahoromatic". Also, watch "Evangelion" to see how Misato and Saori are similar (of course this seems to be a theme in a lot of anime; female authority figures being childish and irresponsible).