Doctor Who Online is reporting that the much anticipated trailer for the 50th Anniversary Special, The Day of the Doctor, may be screened on BBC One on Saturday evening. Originally shown exclusively at the San Diego Comic-Con in July, fans have been disgruntled that the trailer has yet to be aired in the UK. Other sources are suggesting that the trailer will be shown before Atlantis.
The BBC has released a Press Release indicating that a Trailer will be shown prior to Atlantis tonight, however it will not contain any actual footage from the 50th Anniversary special. More details are available here.