Any movie based on a Grant Morrison magnum opus would be good by me- I still want see an "Invisibles" movie- even if the Matrix stole some of the best ideas- a Flex Mentallo or Doom Patrol movie would also be great. If I can't have that, then a "Green Arrow" movie (Mike Grell-style), would be awesome.
I think a Doom Patrol movie would work great in the right hands. That's the one I would really like to see. If they kept the tone dark, the characters could be really cinematic. Also agree on Green Arrow.
Iron Fist would work too.