The Ark - I've all the way back to William Hartnell since this just got released on netflix. Sort of has two adventures in one. First involves the Doctor's companion causing an epidemic by infecting humans of the future who are no longer immune to the common cold. Then they travel to the same place 700 years later to when humans are now slaves to Aliens.
Brain of morbius- This was was actually suprisingly good. Obviously insipred by Frankenstein, a mad scientist build a body out of random alien body parts in order to ressurrect the evil Morbius, a thought to be dead timelord who only now exists as a brain in a jar.
Deadly Assassin- A pretty cool one where The Doctor goes back to Gallifrey to try and prevent an assassination, but instead gets framed for it. Starts off good and ends great, but there's a weird bit in the middle where the Doctor goes into a sort of virtual reality thing.