24. The Daleks (First Doctor)
Now we'll take another step waaay back to 1963, the first season and the first Doctor. While there were many amazing stories during that first season - The Aztecs, The Keys of Marinus, Marco Polo - none can come close to The Daleks, sometimes called The Mutants. The story was the first to feature the Daleks (no duh) and how their hatred for the Doctor all began. When he and his three companions land roughly on Skaro, and need to fix some parts on the TARDIS. Beyond a petrified forest, they spy a large city and head for it, hoping to find someone knowledgeable with machinery. Instead, they walk into a raging war between the Daleks and the peace-loving Thals.
23. Army Of Ghosts/Doomsday (Tenth Doctor)
"This is the story of how I died..." So begins one of the finest series finales, not just of Doctor Who, but of any show ever made. When the Doctor returns to Earth, he finds it inhabited by ghost-like figures. Strangely, the humans don't seem to mind their presence, but he sets out to discover their true nature. He tracks the source of them down to the mysterious Torchwood Institute, where he learns the "ghosts" are actually Cybermen trapped in 'The Void' trying to materialize in our world. Soon they break through, with full-fledged armies, where they declare war on the human race. And the ante is upped even further at the end of the first episode. I won't say what it is here, because either you've seen it and already know, or you haven't seen it and don't want to ending spoiled.