5. The Pandorica Opens
The best cliffhangers either feature an escalation in danger for the main characters or the arrival of a familiar enemy. Clearly wanting to create a very memorable cliffhanger, Steven Moffat ended The Pandorica Opens, the next-to-last episode of Series Five, with both of those things - to an unprecedented degree. As an alliance of the Doctor's greatest enemies traps the Time Lord in an unbreakable prison, Rory the Roman Robot reverts to his programming and shoots his fiancée Amy. Meanwhile, River Song is in the TARDIS as it explodes, subsequently destroying everything in the universe and leaving the Earth alone in existence. Only in Doctor Who, eh? Surely no other episode ends with such scope as this one. There is always the threat of the end of the universe on Doctor Who but before this we had never actually seen it happen. Of course, the whole thing is undone fairly easily in the following episode but that shouldn't - and doesn't - take anything away from the bravura of this moment itself.