Yosuga no sora, nothing beats that thing
Definitely the first anime i watched that's gone too far & definitely sits between ecchi-hentai borderline, some says it's doesn't belong to ecchi anime because it's hentai but some says it doesn't belong to hentai because it's not hentai enough
The countless gratuitous panty shots in Agent AIKa.
Completely unnecessary to the plot, yet the defining attribute to the show's art.
The production values were actually quite good, but it's unfortunate that there's almost nothing to the story, and the only memorable thing about the series was the panty shots...
I actually haven't watched anything solely for the fanservice, I think... Arousal alone has never been enough to hold my interest.
I enjoyed Trinity Seven, How not to Summon a Demon Lord, but that's because I found them hilarious. And Kill la Kill may have fanservice but that doesn't remain the top reason why anyone likes it for long after starting it.
I think the only anime I stuck with for purely superficial reasons was Freezing. I was on the verge of dropping it when HanaKanas character walked in. I watched the whole thing.
On the manga side I'd say Chained Soldier without blinking, but the anime isn't really living up to the potential of the manga.
Definitely Queen's Blade for me, I followed every version up until Rebelion I think? Also Manyu Hikenchou if you enjoy humongous breasts, it's that one where the breast copter gif comes from.
Was extremely underwhelmed when Ayakashi Triangle released censored, and the bluray made it even worse, I still don't get why they even bothered.