Superman Homepage has what appears to be three international posters for Superman Returns that look quite good. Unfortunately the pics are a bit small, so hopefully we’ll be seeing higher resolution versions soon.
Check them out at the link above.
UPDATE: ‘Retroman’ has confirmed that these are indeed the real thing:
A small update the story of new posters that I think may interest you. As it turns they are the real deal and they are now on display at the Cannes film festival.
You view them hanging here and here.
Source: Superman Homepage
