It’s amazing to think now, but Rosario to Vampire was fairly daring for TV show standards back when it first aired. Most mainstream fanservice anime avoided nipples like the plague at this time, instead opting for blank boobs. Rosario to Vampire took things further, particularly in season two.
This was an odd one to say the least. It was part random humor, part seemingly serious storytelling, part weird for the sake of being weird, part nude fanservice, all while being (intentionally?) incoherent throughout. Anyway, the service actually gets pretty intense at times. Good stuff.
For a manga written by a guy (Shoji Sato) who’s day job is writing awesome hentai / doujinshi under the alias INAZUMA, High School of the Dead was shockingly lacking in nipple sightings and loaded with tease.
Widely thought to be the best ecchi series in the last couple years, DXD did something few ecchi series could- appeal to mainstream anime fans while still shoving fully exposed bare breasts in our faces at every turn.