I think there was a thread here, but maybe it was elsewhere, about National Geographic Magazine. If you submit images to them, even if they are not published they get a lot of rights over it. They can use it in books, calendars, whatever. You still own the rights and, as far as I can remember, they don't get exclusivity (but I may be wrong).
I could accept that if an image was published - boy, to be published in NGM! - but I think these terms are unacceptable with unpublished images. Yet, they get many submissions and some awesome images.
Regards,
Adelaide