Linked from
The 13 pages that link to Transposing instrument, each with the reason it gives.
TrumpetRelated: The B-flat trumpet commonly sounds a whole step below its written notes.
Double bassRelated: Double-bass music conventionally sounds an octave below its written pitch.
Tenor saxophoneRelated: Tenor saxophone music is written a major ninth above its sounding pitch.
Concert bandRelated: Many band parts are written at pitches different from those heard.
FlugelhornRelated: The B-flat flugelhorn sounds a whole step below its written notes.