Re. my own stuff : Only ever chucked stuff out that was actually broken. Only regret is losing the brake hanger from my Marzocchi fork.
Re. stuff from bike shops I worked in:
NIB Nuovo Record brake calipers
Umpteen Deore chainsets (with oversize pedal spindle hole)
A mountain of early-mid 80s sprint rims
Michelin Compe skinwall slick tyres en masse - as they kept puncturing. But great for display bikes.
From distributor
2 NIB airlines transmissions.