Of the 75 good anime based on manga, here are the ones that could most profit from an additional anime season:
Nanoha Vivid and/or Strikeforce, the entire thing is currently missing.
Railgun, the most recent arc involving Misaki.
Hayate no Gotoku, Athena's arc, the manga contest arc, or just more Hayate in general.
The World God Only Knows, the gap between season 2 and 3, plus the time travel finale arc.
Fate/Kaleid Liner Drei, in entirety.
Dragon Ball, everything before the appearance of Raditz.
Saki, the semifinals.
Ranma 1/2, the last third of the manga.
Bleach, the war with the quincies.
Sailor Moon, whatever portion of the manga Crystal doesn't cover will still need covering.
Working, everything that comes after season 2 cuts off.
Aishiteruze Baby, the ending.
Claymore, start over starting with the war in the north and this time going to the end.
Berserk, everything after Griffith's transformation.
Yuru Yuri, everything past where season 2 ends.
Shingeki no Kyojin, everything past where season 1 ends.
Chihayafuru, everything past where season 2 ends.
High School of the Dead, everything past where season 1 ends.
Kitakubu, everything past where season 1 ends.
Guyver, everything past where the TV season ends (arrival of the 12 Zoalords)
Break Blade, everything past where Borcuse dies.
Kenichi, everything past wherever the oav's stop covering.
Nichijou, everything past where season 1 ends.
Lucky Star, everything past where season 1 ends.
Soul Eater, from episode 39 of the anime on, this time properly following the manga to the very end.
Flame of Recca, from the end of the tournament until the actual ending.
Bastard, this should really just be redone from scratch, this time following the manga strictly, and obviously much further than where the OAV's cut off.
Gokukoku no Brynhildr, they should redo the 2nd half of this season because they totally mangled the manga adaption starting around there. Give the series enough episodes to tell the story correctly.
Jojo's Bizarre Adventure, they still haven't promised to adapt manga parts 4-8 yet.
Sakura Trick, moar kissing!
Mikakunin de Shinkoukei, everything past where season 1 ends.
Btooom!, everything past where season 1 ends.
To Love ru, the rest of the Darkness storyline, and a non-filler rendition of the original would help.
H2, the vast majority of this tale hasn't yet been told.
Gakuen Alice, same as H2.
Alien Nine, may as well cover the ending, it's a short manga anyway.
RG Veda, same as alien nine.
Negima, this needs a total remake with a much larger length and budget covering the story from beginning to end.
39 shows aren't being handled right. If I had to rank the top ten projects in need of support that don't seem to be getting any, I would say:
2. Nanoha Vivid.
3. Dragon Ball
5. The World God Only Knows
7. Ranma 1/2
8. Hayate no Gotoku
All 39 shows could use help, but some of them still have a realistic chance of receiving support from anime studios down the line, like Fate or Railgun. Others wouldn't improve much even if you did help them. But these ten really stick in the craw. It's hard to imagine any of them will get animated anymore, even though the benefits to fandom and art in general would be tremendous. This is really the time for a charitable billionaire to step in and get this ball rolling. We're leaving the greatest works of art of all time rotting in the fields here. Whether these works operate at a loss or a profit doesn't matter -- we're talking shows that are better than Shakespeare or the Sistine Chapel here, and they were state supported. Why not a Dragon Ball remake?