Genesis - The Lamb Lies Down on Broadway - deserves a mention, even if it could have 'happily' lost the odd track.... (likewise The Beatles [white album] mentioned above)
Probably The River (Springsteen) for me (even that could have easily lost a couple of tracks [or, preferably, had them substituted for other stuff he had 'in the can'].
'Officially' the answer is probably Dylan's Blonde on Blonde....