sigur wrote...
Thirteen Senses - Into The Fire
Sufjan Stevens - Romulus
Sufjan Stevens - Casimir Pulaski Day
Interpol - Untitled
Joseph Arthur - In The Sun
Bon Iver - Skinny Love
Antony and the Johnsons - Hope There's Someone
Casiotone For The Painfully Alone - Young Shields
Elliott Smith - Between The Bars // E.S in general
Elliott Smith - Angeles
Flowers From The Man Who Shot Your Cousin - Lay Down Your Arms
Israel Kamakawiwo'ole - Somewhere Over The Rainbow/What A Wonderful World // Happy sad song
Cat Power // Most of her songs
Sigur ròs // post-rock beauty
Classical music !
I can't believe you didn't mention "For the Widows!"
And for Post-rock beauty, I think Explosions in the Sky better meet the qualifications for "sad music"