We don't know much of anything about the upcoming 'Superman' film for certain, except that Zack Snyder is directing it and Henry Cavill will don the iconic red and blue tights. That hasn't stopped the rumor mill from churning out numerous casting stories in the past week, including two intriguing, but most likely improbable, gossip bits about who might appear alongside the Man of Steel.

First up is news from THR's Heat Vision blog. Their sources are saying that Snyder and producer Christopher Nolan have marked 'Lord of the Rings' star Viggo Mortensen as a person of interest to play the villainous General Zod.

Zod, who originally appeared in the comics, is best known as the lead baddie in 'Superman II,' where he was portrayed by Terence Stamp. Mortensen would make for an interesting choice, for sure, although we can't shake the feeling it feels a bit safe.

Mortensen isn't a lock for the part at this point, plus he's still in the running for Universal's 'Snow White and the Huntsman.' If he lands that part, it seems unlikely that he'd be able to shoot both it and 'Superman' -- at least not without major scheduling shifts.

Hit the jump for more casting rumors.

The 'Superman' news doesn't end there, though. Moviehole's Hollywood Resnorter blog mentions that Daniel Day-Lewis is also on the film's wish list of stars. This seems like an even bigger stretch than Mortensen, given that DDL has often shied away from big-budget studio films. It doesn't seem likely that he'd break with that trend by jumping right into a superhero film, which is about as mainstream, big budget and non-challenging as you can get.

The rumors are very vague at this point, with no real word on whom the actor would even play if he were to join the production. This has led to speculation that he might also be in the running to portray General Zod, or perhaps Zod's henchman, Non. Day-Lewis seems vastly overqualified for both of these roles, but he could be fun as Zod.

In other casting news, Movieweb says it appears as though Shia LaBeouf has emerged as the front-runner to replace Matt Damon as Jason Bourne in Universal's 'The Bourne Legacy.' If he does eventually land the part, he'll have beaten out actors like Jake Gyllenhaal, Tobey Maguire, Garret Hedlund and Kellan Lutz.

The production is said to be looking for actors in their mid-20s to early-30s, which puts Labeouf right in the sweet spot. LaBeouf might have the inside track for the gig, given that he worked with producer Frank Marshall on 2008's 'Indiana Jones and the Kingdom of the Crystal Skull.' No official decision has been made yet, but Universal hopes to get the production rolling later this spring. 'The Bourne Legacy' is due to hit theaters on Aug. 3, 2012.

As always, take these rumors with a grain of salt. Hollywood loves to play the name game with big productions, and then entirely different actors are cast in the roles. That said, what do you think of these potential choices? Would any of these actors entice you into seeing these films? Whom would you cast instead?