During the Great Superman Drought of 1987-2006, there were plenty of attempts to revive the Man of Steel that never really came to light, and other plans that fell through as well. Based on what we know, which would you have been most interested in seeing?
1. The Original Superman III: Ilya Salkind's initial treatment for Superman III had Supergirl being raised by Brainiac, who eventually wants to marry her, because I guess the Westermarck effect doesn't exist in Coulans. Coming to Earth, she instead falls in love with Superman, with the feeling being mutual (Salkind even notes that there's a scene where they make sure they're not related), and Brainiac comes to Earth to try and steal her back. Also there's time travel back to the middle ages so Superman and Brainiac could duel on horseback, and Mxyzptlk shows up basically out of nowhere as co-villain for some reason, with plans for either the ending of III or Superman IV to cover the wedding of Superman and Supergirl. Here's a link to a copy of his treatment.
2. Superman V/Superman Reborn: Co-written by Ilya Salkind, Cary Bates and Mark Jones after the rights reverted to the Salkind brothers from Cannon Films - the visionaries behind Superman IV - it's known that they completed two drafts of this script (one of which is readable here). It would have seen Reeve reprising his role for a confrontation with Brainiac in which Superman dies in battle (years before the actual big Death of Superman), only to be revived in Kandor and given an opportunity to connect with his Kryptonian roots while recuperating for his final showdown with the villain.
3. Superman Reborn: Having gone through a handful of drafts under Jonathan Lemkin and Gregory Poirer, plans included the likes of Superman dying and being reborn/growing back to normal in 3 weeks through the virgin birth of Lois Lane, going to a psychiatrist about his relationship troubles with Lois (and after that last plot point, I get where he's coming from), and being killed by a Kryptonite-blooded Doomsday before being resurrected by Cadmus (an alien, not the organization) to battle Brainiac and regain his powers through mastering the mental discipline of "Phin-Yar", the true source of his abilities. Parasite and Silver Banshee may also have appeared.
4. Superman Lives: You know about this one. Everyone knows about this one. Nic Cage, Tim Burton, Kevin Smith, the giant spider, Christopher Walken as Brainiac, all that. If you don't - and really, even if you do - I can't recommend enough checking out the documentary The Death of Superman Lives, chronicling the rise and fall of this truly astonishing dream of producer/noted madman Jon Peters.
5. Batman vs. Superman: The more things change, eh? Planned to be directed by Wolfgang Petersen and written by Akiva Goldsman, it was set in a near future where pretty much everything's gone to hell (Dick Grayson, Jim Gordon and Alfred are all dead, Bruce is retired and Lois is divorcing Clark), and Bruce Wayne wakes up the morning after his wedding to find his new wife dead courtesy of the Joker. Superman (who's starting to strike up a new relationship with Lana) has to stop Batman from killing his old enemy, with Lex Luthor of course having plans behind the scenes. There were talks of Josh Hartnett playing Superman, but the main candidate was in fact Christian Bale, who was simultaneously being considered for Darren Aronofsky's aborted Batman: Year One. That Goldsman was involved in both this and I Am Legend is in fact the reason for the Superman Vs. Batman poster appearing in that movie. Here's the script for those interested; it's frankly pretty bad, but there's enough crazy stuff in there for it to be worth a look-see.
6. Superman: Flyby: JJ Abrams' proposed Superman reboot (I haven't seen the new Star Wars yet, but that's what prompted this) in which Superman must battle a Kryptonian army attacking the Earth led by his cousin Ty-Zor, I don't think this gets enough credit relative to Superman Lives in terms of being the craziest one that very nearly happened. Some bullet points: Krypton lives with Kal-El being sent to Earth to fulfill his destiny as a chosen one, Clark has PTSD and panic attacks from accidentally nearly killing a guy who tried to rape his mom when he was six (consequentially, the nervous Clark Kent act is actually his real personality in here, with Superman being pretty much 100% an act on his part until near the end), the Superman costume is alive, Clark's poop is maybe radioactive, Jimmy is the most astonishingly stereotypical gay guy imaginable (at one point in the movie while sobbing, he notes "Guys, this is so heartbreaking, I feel, like, hormonal--"), Superman dies but then Jor-El kills himself to go meet Superman in Heaven to tell him to come back to life so Superman does, and Luthor turns out to be a Kryptonian sleeper agent, because of course he does, with Superman going to spend the next movie on Krypton with presumably no powers. Henry Cavill was in talks to play Superman (there's actually a photo of his screentest floating around the internet that's not hard to find) along with the likes of Jared Padalecki, Ashton Kutcher, Justin Timberlake and Josh Harnett, with Matt Bomer apparently the final choice. Anthony Hopkins was apparently going to play Jor-El with Robert Downey Jr. or Johnny Depp as Lex Luthor, Shia LaBeouf as Jimmy Olsen, and Scarlett Johannson or Selma Blair as Lois Lane, with either McG or Brett Ratner directing. Here's one draft I've seen, here's another.
7. Superman: The Man of Steel (Superman Returns sequel): Pretty much the only concrete things we know about this are the title and that Singer's said he would've wanted Darkseid as the villain. One rumored plan had Brainiac as the villain posing as a Kryptonian savior of the Earth handling the 'real' problems before being revealed as intending to destroy the world, culminating in, I **** you not, Brainiac possessing Superman's son Jason and Superman being forced to break his kid's neck to save the day. This proposed plot may be entirely made up, but I prefer to believe every word of it, because that is hilarious.
Pick your poison!
EDIT, thanks to Myskin reminding me
8. Superman (Mark Millar/Matthew Vaughn): Millar's proposed Superman trilogy, filmed in unison in the same manner as Lord of the Rings, would've begun 1,000 years before the death of Krypton, and ended 5 billion years in the future with Superman dying peacefully as the last man in the world as the sun goes red and swallows the Earth, telling the ultimate story of Superman's life. He ended up disqualified due to his official ties to Marvel, but he had planned on Matthew Vaughn directing, and has repeatedly noted he one day intends to adapt the story as an OGN.