I saw this and couldn't help, but shout out in my head MERU PERI by Matsuri Hino !!
Another one that just came to me is Battle Royale, with the success of the book, manga, and movie it's a bit surprising they haven't attempted to create an anime series based of it. It has enough appeal, story, characters, and settings to make easily a 12 episodes series I would think.
Kimi No Iru Machi for sure, although I would want a good company to do it not like the one that did Suzuka.
Meru Puri and God Child would both be awesome as anime's.
Shounen Shikaron is something that I found completely by chance and fell deeply in love with~. It has such an original concept and fun characters. I'm not saying that it deserves an anime, but it definitely needs to be licensed in the US, so I can at least buy it!!
Even though the whole demon hunter thing is done to death, I love the characters and the aesthetics of gothic lolita fashion.
Oh Yeah....and I would die for a Bizenghast anime and a Black Rock Shooter Manga series and then a full anime series based on the manga. I'm so needy
Here's what should have an ANIME
* Aflame Inferno
* Unbalance X Unbalance
* Zero In
* Ubel Blatt
Yotsuba! really should get an anime adaptation, it's the only manga I've partially read that didn't have one.
I'm sure Rin-ne by Rumiko Takahashi will eventually be made into an anime. Other then that, maybe Future Retro Hero or some more Outlawstar.