Here you can find some songs that do not appear on any official albums. They only exist on singles, videos, compilations or bootlegs.
I haven't included the different mixes of songs.

Afghan
Argiers
Blue Peter
Bones
Cuckoo Song
Don Alfonso
Early Stages
First Excursion
Froggy Went A-Courting
Guilty
In Dulci Jubilo
In Dulci Jubilo (For Maureen)
In The Pool
Indian Lake
Jungle Gardenia
Legend
Mike's Reel
Mistake
Music For The Video Wall
The Path
Pictures In The Dark
Pipe Tune
Portsmouth
Rite Of Man
Shine
Silent Night
The Song Of The Boat Men
The Spectral Army
The Trap
Vivaldi Concerto in C
Waldberg (The Peak)
William Tell Overture
Wrekorder Wrondo