A lot of people will say it would be hard to adapt, but the Sandman (and more Vertigo down the road), if done right, would be amazing. It's a bit more niche and is less well known amongst general audiences, but if the last decade has proven anything, it's that you don't need Superman, Batman, or Spiderman to be successful. For me, the otherworldly scale of the series and the depth of its enigmatic characters are unmatched by most other comic book properties.