Well let's see... The ones I can remember are The Moon Base (2nd Doctor), Paradise Towers & Battlefield (7th Doctor), and . . . I think one other from Patrick Troughton's run, but I can't remember anything about it. I think it was another Cybermen episode.

ETA: What I'd really like to do is figure out where I should start with Tom Baker, since he's the one with the largest number of episodes during the classic era.