Metal Gear Solid. Madhouse adapting the Shadow Moses incident would be like a dream come true. I'm actually really surprised that hasn't happened already. Marvel Vs. Capcom. Could make a cool movie or OVA, if they were faithful with the designs like in the game. Obviously screw trying the story make sense, just make it bad ass.
"If you tremble with indignation at every injustice, then you are a comrade of mine"
When the union's inspiration through the workers' blood shall run
There can be no power greater anywhere beneath the sun
Yet what force on earth is weaker than the feeble strength of one
For the Union makes us strong
I reckon Skullgirls would make a great anime.
The game itself has references from Panty and Stocking,FMA,HOTD,Durarara,Evangelion,Vocaloid,Hellsing,Black★Rock Shooter,Naruto,Soul Eater, and a few others which was nice to see
I love the Langrisser game series; it has the great character designs by Satoshi Urushihara, an epic storyline as the five games are intertwined with one another, and an awesome cast of male and female characters. It would make an awesome anime series.
An anime adaptation of Sakura Wars 4 would be nice too as it unites the original Teikoku Hanagumi with the ones from Paris, I love seeing both Sakura and Erica in action together.