26. Army Of Ghosts/Doomsday
These episodes form one of those rare Doctor Who stories which is so good that it's been etched into the public consciousness. Even if you don't watch the show, the chances are you know of the moment when the Doctor and Rose say goodbye on the shores of Bad Wolf Bay. And the rest of the story ain't half bad, either. Series 2's big bad - the mysterious Torchwood - are revealed as a Doctor-hunting alien-busting organisation and, most importantly, fans are finally given the big ol' fight between the Daleks and the Cybermen they've been waiting for (resulting in some brilliantly bitchy lines from both monsters). Even now, this is probably the story that all Doctor Who finales are judged against.