40. The Three Doctors (First, Second, and Third Doctors)
When 1973 rolled around, the writers of Doctor Who determined it was time to commemorate the beginning of the tenth year of Doctor Who's run on the air. How best to do that? Simple. Have (at the time) all the Doctors together in one story. The story goes that on Gallifrey, someone is draining all the power away from the Time Lords through a black hole. Intent on stopping this, but unable to do so themselves due to being under siege, the Time Lords see fit to call on the Doctor, who is currently exiled on Earth. But not just the one Doctor, his two previous incarnations as well. The two shining moments from this story are the introduction of Omega, and giving us a chance to see Patrick Troughton back in action as the second Doctor.
39. Ghost Light (Seventh Doctor)
Another serial from the final season of the original show, this three-part story was in fact the last one filmed. And what a doozy it is! The story follows the seventh Doctor and Ace visiting a house that she burns down later in the future. While there, they find many strange goings-on (of course, when does the Doctor not?). The first two episodes of the serial are among the absolute best television you'll ever see, while in the third episode the writing and plot and all get kind of undone and messy. Nonetheless, the beginning two-thirds are good enough for inclusion on the list.