OK, so recapping what we did on Gabbly on the subject:
Brad Pitt or Jude Law as Ozymandias. They both fit the pretty blond boy image and are both good actors, so it would work perfectly. I'd prefer Pitt, personally, but we know that Law is a Watchmen fan and has already apparently been in contact with Snyder about the role, so he's more likely.
The Comedian we had a lot of trouble casting, because he has to be an older guy but still tough and so forth. I think the best idea we came up with was Daniel Day-Lewis with some makeup to make him look a bit older. Other ideas were Kurt Russell, Burt Reynolds (a little too old at this point), Clint Eastwood (certainly tough, but too skinny), and Jon Voight (too pudgy).
Nite Owl I think is a less critical role, because even though he's one of the major characters there's not quite as much nuance to him as some of the others. Emilio's idea was Dennis Quaid but mine was Phillip Seymour Hoffman, which I liked because Nite Owl is depicted as going a little soft in his retirement.
Dr. Manhattan is easy because he'll presumably be all CG with somebody's voice over it. They'll probably even use computer effects on the voice too to make it more creepy, alien-sounding. We decided it would be the best role for Gerard Butler, who is supposedly involved in an unnamed role, but I think Hugo Weaving could do well here.
Rorschach is a tough one too, but Bacon works pretty well, and the other idea we had was Hugh Jackman.
Silk Spectre is I think the most critical role in whether or not this film is a pile of shit, because it's the easiest one for them to go Hollywood and cast Jessica Alba or somebody equally horrible and ruin the whole thing. The one I came up with was Rachel Weisz, because she's the right age, a brunette (although it's not like that matters too much), and she can actually act. I am a little biased, though.
That's what we came up with in the hour or so we discussed this on Gabbly. I came up with Dustin Hoffman as Nite Owl afterwards, but he's probably too old at this point.