Really, they change too much for this to be definitive. I'm also not listing them in order because that would be a headache. None of these are "flavor of the month" numbers, these are all songs I've listened to time and again.

"Alice" - Cocteau Twins https://www.youtube.com/watch?v=hxSMckGfQ2k

"Desolate Ways" - Morbid Angel https://www.youtube.com/watch?v=iZPKBAnkEaE

"Nights in White Satin" - The Moody Blues https://www.youtube.com/watch?v=IAjGdmFKf8E

"Clothes of Sand" - Nick Drake https://www.youtube.com/watch?v=oE6PfDsYVjA

"C'est La Vie" - Emerson, Lake & Palmer (studio version) https://www.youtube.com/watch?v=2SCmchJTPPo

"Scarborough Fair" - traditional, but my favorite version is by Simon and Garfunkel https://www.youtube.com/watch?v=BYQaD2CAi9A

"Stinkfist" - Tool https://www.youtube.com/watch?v=07pLGIgyfjw

"Breathe" - Pink Floyd https://www.youtube.com/watch?v=mrojrDCI02k

"Who Murdered The Minutes" - Joan Baez https://www.youtube.com/watch?v=7pCADFnDrlg

"The Wind that Shakes the Barley" - traditional, my favorite performance is by Lisa Gerrard https://www.youtube.com/watch?v=FkBQggRBqEY