With being a big fan of electronic music I thought the music on Classic Dr Who was great and added to the atmosphere of the show. Here is my list of some of my all time favourite incidental scores of Classic Who.
Mindwarp - Richard Hartley
Planet of Fire - Peter Howell
Caves of Androzani - Roger Limb
Revelation of the Daleks - Roger Limb
Vengeance on Varos - Jonathan Gibbs
Enlightenment - Malcolm Clarke
The Leisure Hive - Peter Howell
Logopolis - Paddy Kingsland
City of Death - Dudley Simpson
Jonathan Gibbs - Mark of the Rani
Time and the Rani - Keff McCulloch
The Mysterious Planet - Dominic Glynn
The Greatest Show in the Galaxy - Mark Ayres
Mindwarp - Richard Hartley
Planet of Fire - Peter Howell
Caves of Androzani - Roger Limb
Revelation of the Daleks - Roger Limb
Vengeance on Varos - Jonathan Gibbs
Enlightenment - Malcolm Clarke
The Leisure Hive - Peter Howell
Logopolis - Paddy Kingsland
City of Death - Dudley Simpson
Jonathan Gibbs - Mark of the Rani
Time and the Rani - Keff McCulloch
The Mysterious Planet - Dominic Glynn
The Greatest Show in the Galaxy - Mark Ayres

I know what I mean. It's used in the scene where Tom and Elisabeth are skulking outside the house trying to avoid being seen and ducking below the windows in 'Pyramids...' Variations occasionally cropped up and I related it to Tom's Doctor.