Studio Kimigabuchi makes hentai doujinshi with more than just the "usual" content.
Their most notable doujin is probably the Neon Genesis Evangelion RE-TAKE series 00-04 + After, featuring a whole new ending of the legendary psychotic Evangelion series. Some fans consider this the possibly best NGE ending ever. The doujin series even received its very own soundtrack.
Some other works: Higurashi no Naku You ni Code Eross Negimaru