Those "perfect" (non-metal) albums...

My Bloody Valentine - loveless
REM - Dead Letter Office

and all nine of Beethoven's symphonies... they mix well with Burzum and first album Incantation.
 
Belle and Sebastian - Dear Catastrophe Waitress
Rilo Kiley - More Adventurous
Nick Drake - Five Leaves Left
Radiohead - The bends
Jeff Buckley - Grace