Doujins are basically like fan-comics/manga. Let's discuss some Madoka Magica doujins. You can suggest NSFW doujins but please don't go into detail about them, don't link to them, and put a warning that they are NSFW.
Here's some of my favorite doujins:
Homura x Madoka (Main pair):
http://dynasty-scans.com/chapters/theres_only_one_thing_i_want_to_tell_youThis is a yuri schoolgirl AU. Homura is the popular girl in school and she's always getting love confessions from people (and always turning them down). Madoka is secretly in love with her and worries that Homura will end up going out with someone else. After a bit of angst, Madoka finally confesses her feelings and we get a sweet yuri romance.
Madoka-san, Please
Warning:NSFW
This a hilarious manga where Madoka is invited over to Akuma Homura's house and fantasizes about different
ways that Homura could take advantage of her. She gets disappointed and frustrated though when her host
acts like a perfect angel despite all her talk of being a "demon".
I Absolutely Won't Let Go Anymore
Warning: Slightly NSFW
A cute manga about both Homura and Akuma Homura giving Madoka and Madokami a coat when they say they are cold. The manga is mostly SFW, but the last page is NSFW so I didn't link to it to be on the safe side.
http://dynasty-scans.com/chapters/kiss_or_chocolateAkuma Homura teases Madoka about chocolates on Valentines Day in order to steal a kiss out of her. Cute and hot, but still SFW.
Tatami Ouroboros Duo
Warning: Very NSFW
Akuma Homura and Madokami live together in a small apartment. They have the sweetest romance ever and are just like a marired couple. However, besides the sweet moments, their relationship also includes "adult aspects", making the manga very NSFW, so I can't link to it directly. But besides all the smut, the relationship between the two is very sweet, so if you are old enough to read that kind of thing and don't mind it, I highly reccomend giving it a read. It's my favorite of all the doujins so far because it has Akuma Homura and Madokami living happily together in a healthy
relationship which is what I really needed to cure my broken heart after the end of Rebellion.
Nukumori o Wakeainagara Futari no Kyori o Chijimeyou
Warning: Very NSFW
An AU where Madoka has gone insane and killed off everyone in the world except for Homura, who she hallucinates is a cat. In a post apococalpyse world, Madoka and cat-girl Homura do lewd things together before Homura finally resets the timeline. It's very deranged, but oddly intriguing do to its unique setting.
http://dynasty-scans.com/chapters/how_much_i_like_youA short series of adorable images where chibi lizard Homura (according to Rebellion handbook info and the concept movie Akuma Homura has some kind of connection to a lizard) and Madoka express how much they love each other in adorable and innocent/pure ways.
http://dynasty-scans.com/chapters/the_lie_that_melts_into_the_rainHomura and Madoka share an umbrella in the rain and Madoka invites Homura to stay the night at her house so she doesn't have to walk home in the rain.
http://dynasty-scans.com/chapters/before_a_halloween_night_outMadoka and Homura are going trick-or-treating and Madoka helps Homura with her ghost costume.
http://dynasty-scans.com/chapters/its_christmas_a_homumado_mangaAkuma Homura and Madoka spend Christmas together and confess their feelings, but Madoka warns that she won't be able to remember her confession the next day even thoug she returns Homura's feelings.
http://dynasty-scans.com/chapters/the_rewind_girlThis manga contains two stories. The first is a drama about Homura killing a cat that was going to put Madoka's life in danger if she saved it. Madoka is horrified after that and Homura has to reset the timeline again to make things right between them. The second is a comedy where Homura is being a bit of perv taking pictures of Madoka and checking out her legs while mistakenly believing that she has time paused. It turns out she was out of sand and Madoka ends up unleashing the cops on her, so she has to reset time again.
Untitled Ecchi HomuMado
Warning:NSFW
Akuma Homura being a flirt and a perv towards Madoka. Btw, yes, that's the real title. The author is Homura-chu. Most of the manga is more suggestive than anything, but the second to last page really gets into NSFW territory and the last page is NSFW as well even though you can't actually see anything in that one, so I can't link it.
http://dynasty-scans.com/chapters/10_03Madoka and Homura are all grown up. Madoka is a teacher and one of her students wants to confess his feelings to her. Of course, this makes Homura jealous and her "devil" side comes out causing her to pretend like she's kissing Madoka in front of the boy.
Mami x Nagisa (Main pair):
http://dynasty-scans.com/chapters/maminagi_mangaThis one's so cute. It has more a big-sis little sis kind of vibe between Mami and Nagisa though. Mami goes to school for Nagisa on "Meet The Parents" day at Nagisa's school and they get in a fight about it, but then they make up. It's so cute, fluffy, and innocent.
http://dynasty-scans.com/chapters/raison_detre_no_arikaThis doujin gives Nagisa and Mami's relationship in Rebellion a backstory.
Kyoko x Sayaka(Main pair):
http://dynasty-scans.com/chapters/we_found_our_lost_futureA very sweet AU where all the girls are alive again and no longer witches and Madoka is no longer a goddess who can't be seen. It has some sweet minor HomuMado moments, but the main focus of the manga is abou Kyoko and Sakaya getting a second chance to expand on their friendship. It's mostly platonic best friend stuff in the case of both pairings.
We'll Meet When Life Comes Full Circle
Warning:NSFW
This is mostly a Kyoko x Sayaka manga, but it does have a decent amount of Mami x Nagisa and some minor Madoka x Homura in it. Kyoko and Sayaka romance each other in Homura's witches barrier. Meanwhile, Nagisa tries to get Mami to treat her seriously instead of like a little kid. Homura and Madoka play a minor part, mostly just there as part of some lewd comedy moments sadly.
Multiple Pairings:
http://dynasty-scans.com/chapters/piyo_piyo_magicaA series of one-shots about Kyoko x Sayaka, Mami x Nagisa, and Homura x Madoka. The first one shot is a comedy where Kyoko is confused because she thinks Sayaka's pregnant and that she's the one that made her pregnant and she doesn't know how that's possible because not only have they never done anything, but they're both girls. Spoiler but not really since the reader knows from the beginning:Sayaka's just fat and on a diet.
The second oneshot is a comedy about Mami and Nagisa. Mami wants Nagisa to cut back on eating cheese to only once a day because its bad for her. They get in an agrument about it and eventually Nagisa pulls the little sister flattery act on her "Mami Onee-chan".
The third one and last one is a bittersweet drama between Akuma Homura and Madoka. I was kind of disappointed that it wasn't a comedy like the other two so it was my least favorite of the one-shots,but it was alright.
http://dynasty-scans.com/chapters/kiss_chainAdorable series of images of the girls kissing. No text, but you don't really need diologue to get what's happening. Pairings include Mami x Nagisa, Mami x Kyoko, Sayaka x Kyoko, Sayaka x Madoka, Homura x Madoka, and Akuma Homura x Madokami (who are both shown as separate from regular Madoka and Homura here and are shown pushing them together.)