Pelswick. I'm not surprised there were no fics when I checked, but it would've been nice to see one or two. But then, that'd require someone knowing the show better than I do and having the drive to write...
Editor of Posts
I had a good chuckle checking out all the Bambi crossover fics (all ten of them). Bambi works very well for crossovers since it's never stated where or in what kind of universe the forest is; so you think people wouldn't just insert two gay fawns named Kirk and Spock instead.
Also, turns out Estonian mythology is the most popular mythology after Greek, Norse, Egyptian and Japanese. Who knew.
edited 5th Jan '15 1:46:06 PM by Druplesnubb
Pretty much every not-so popular book I have ever read. 
There is much fanfic about Kvothe and Tempi from the Kingkiller series, but I would like to see more about the Adem. The author just invented one very interesting native tribe, and then only used it as magical natives to make his pet Kvothe even more awesome. There's a lot of lost potential in that.
Edit: Stupid me, the fanfics are all about Kvothe and BAST. Tempi is Adem, and I would actually like to read about him.
edited 9th Mar '15 10:15:37 AM by Gowan
Professional Recluse
Ah someone else who's read Greywalker, considering the subject state I'm pretty astonished that it hasn't had some crossover with The Dresdon Files or Magic _____.
Stoned hippie without the stoned. Or the hippie. My AO3 Page, grab a chair and relax.
Paranatural.
Kind of cheating, as it has 20, but it deserves so much more.
This War Of Mine. It kinda needs a fandom. Lots of people enjoy the game and buying it raises donations for war child. If this really has like a legit fandom, then it would be surprising amounts on tumblr. And we're talking about tumblr here. That place has almost everything.
edited 10th Mar '15 12:48:18 AM by deadwaste
Jer gets all the girls
Conditions of Great Detectives. Like some people above, I'm not really surprised that a 10-episode Japanese drama doesn't have any fanfics, but it's still annoying
Everybody's all "Jerry's old and feeble" till they see him run down a skyscraper and hijack a helicopter mid-flight.
Braids From S286 Not Included
Here be Monsters. Actually, its "fandom" consists of people who don't care much about the story, but rather, the gameplay. I so want to see a fic that picks up from the last cliffhanger, since it's been more than six months since the last storyline update.
EDIT: And as of earlier this October, it has shut down.
edited 24th Oct '15 7:00:48 AM by TroperNo9001
"Rarity, are you okay? We gotta get you and your friends outta here soon!"
Marathon.
The world will look up and shout "Save us", and I'll look down and whisper "Too bad, Waluigi Time" Vote Loki 2016
Magus
EVE Online. Sure, it doesn't precisely lend itself well to fanfic, but I'm sure it could be done by those of greater skill.
Also, Homeworld. Seriously, I've seen one fic of any length - admittedly, it was an amazing fic, but still.
The Culture. I was disappointed to see such an interesting series have small amounts of fanfiction.
The Breakfast Club. I mean, the movie is so freaking awesome and there are so many fanfic opportunities... yet the only fanfics i can find are awful "what happened on monday" fics where the same thing happens every time.
Advance towards me, brethren.
The Drifters manga since one can write fanfics for public domain figures who made an impact on history in terms of standing alongside the Drifters or the Offscourings.
Now that someone subbed the first two Next Generation Patlabor movies, the Patlabor franchise deserves more fanfics more than ever.
Why aren't you laughing?
Haven't check on to see if there are any, but I would have to say Dungeon of the Endless.
Fun video game series, and it has a lot of fan fic material with all the eccentric characters and interaction with one another. I am amaze I have seen any stories of this game yet (maybe its brother series Endless Space and Endless Legend have some fan fics).
The future of warfare in UC.
Yeah. Well, Law & Order: Mobile Police crossover. Let's make it happen!
Nous restons ici.
That seems to be an unheard idea so far.
Ever 17. Which has 3.
My AO3. Results may vary
More Kane and Lynch. As of now, it's around 9.
hey i dunno, why don't you tell me
Titan A.E. has a few, but as far as I can tell, nobody thus far has seen fit to venture an opinion on just what the hell that thing Gune made in his sleep actually does. It has a button. The button was not pressed. And nobody cares enough to wonder?
edited 18th Aug '15 3:27:25 PM by Knowlessman
i care but i'm restless, i'm here but i'm really gone, i'm wrong and i'm sorry, baby
Neal Shusterman.
I would also be interested in reading some decent Crest of the Stars fiction. Let me sigh wistfully at the thought of the blue-haired uniformed chicks Space Humans.
Has anyone ever gone to FFN
and looked for a fandom, only to discover that no one has published any stories for it? Personally, I've been quite disappointed to find that Recettear has no fanfics, nor do the novel series Greywalker, Codex Alera, or Deathstalker. At least there's a few for Zelazny's Book Of Amber and the Night Side.
That’s the epitome of privilege right there, not considering armed nazis a threat to your life. - Silasw