The Old Doctor: Jonathan's Quick Intro Course

Of course, any serious Who fan will watch all 50 years' worth of the series. But to come up to speed on back-references to the pre-2000 series that come up in the post-2005 series, here is a suggested minimal list of episodes featuring Doctors 1 to 8 which will familiarize you with the back story sufficiently to appreciate more of the allusions.

Note: I'm not a fan of Six (I blame the writers and producers more than the actor for the poor quality of his era). So I picked the story in which Two also appears... it does have some pretty bad moments though.

Dr. No. Title Highlights
1 An Unearthly Child (first episode only) Tardis, Totter's Lane
2 The Invasion UNIT, Cybermen, Great Intel.
3 Spearhead from Space Autons
3 The Sea Devils (and/or The Daemons) Silurians, Master, UNIT
3 The Time Warrior Sarah Jane, Sontarans
3 Day of the Daleks Daleks
3 Frontier in Space Daleks, Master
4 (Last few minutes of Planet of Evil) Sarah Jane leaves - for now!
4 Deadly Assassin Time Lords
4 Genesis of the Daleks Daleks, Davros
4 City of Death Romana; Douglas Adams script
4 (Logopolis last half hour) Regeneration at Jodrell Bank
5 (Castrovalva first half hour) Regeneration at Jodrell, ctd.
5Resurrection of the Daleks Daleks, Davros
6The Two Doctors Jamie, 2nd Doctor
7 Remembrance of the Daleks Daleks, Totter's Lane
7 Battlefield UNIT
8 Dr Who TV Movie Regeneration, Master
W Night of the Doctor (2013 minisode) 8th doctor regenerates to John Hurt