With Season 5 due in the next nine days, I'm hoping to speed this list up.
16: Revelation Of The Daleks (6th Doctor)
Davros can get some pretty hit and miss moments in the series but for me, this is a fine story for him. He's at his ruthless best in this one with his solution for famine and his pithy black humour (actually the whole story is) works remarkably well for this one. Even the annoying DJ becomes someone to care about as he gets exterminated.
17: Logopolis (4th Doctor)
After seven years, Tom Baker's reign on the series had to come to an end. Okay, falling from a great big heigth might not be the best way to regenerate but the story is wonderful (if a tad complicated). You've got the Master getting used to his new body, a depature of a Doctor, Nyssa becoming a full time companion and the introduction of Tegan. Quite a busy story really.
18: Frontier In Space (3rd Doctor)
Another underrated story but one I recently acquired on DVD and enjoyed a lot. The Master and Daleks working together to cause war between Earth and Draconia. Jo Grant mentally outsmarting the Master as well as the Doctor being left in a rough state at the end. Yeah, this one certainly knew what to do with it's six episodes.
19: Survival (7th Doctor)
I know as series finales it's not perfect but it's actually better than some of the series enders for shows that had time and preparation to brings to an end. It's got the Master in one of his better stories, an interesting use of 'survival of the fittest' and the final exchange between the Doctor and Ace is a little too perfect for words.
20: The Invasion (2nd Doctor)
As Cybermen stories go, it's a bleeding classic even if you do have to wait halfway through the thing for them to show up. Even seeing the first and fourth episodes in animation doesn't deter the enjoyment of this one. And that scene where the Doctor is running from being shot at is quite funny. Plus the Brigadier and Benton for the win. And Jamie. And Zoe. And yes, Isobel tooo of course.