If we're just talking doujinshi, then there are a couple of artists and series I recommend.
Amano Ameno - his stuff looks great, the girls are drawn beautifully, and he also likes his girls in bondage and scat.
Saigado - Any of his stuff looks great and sexy, girls are beautifully well drawn.
Asuka series - Wow. As far as I'm concerned, this is the ultimate Asuka doujinshi that NGE can offer. It's Asuka in all sorts of compromising situations and the artwork is fantastic. (looks exactly like the anime, but with more details of course.)
The final winner: Dead or Alive series
Fire Wire DOA - I can't describe how great this doujinshi is. Ayane and Kasumi are fucked over and over by Kasumi's clone and her ninjas. Not translated in english, but all the same, I love it. Artwork is grade A and features light bondage.
Rei DOA - It's like Fire Wire, but in modern times and both Ayane and Kasumi are again put into compromising situations by other high school students. Made by the same mangaka as Fire Wire, artwork is grade A, and is also translated by FAKKU, except the fourth chapter "Surge".