good thread idea, but hard to know what defines "hidden" since we probably know them all so well
but here goes:
ATAP
Because you're mine ( and maybe several other mamouna tracks, most of which i like, and i think they're nearly all hidden, since so few units were sold)
as the world turns
she's leaving home (one of kate bush's favourite BF numbers, btw, alongside RM1)
help me
love war
blinded by the life
funny how time slips away (great vocal)
zamba
39 steps (one of the eno mix versions)