To me, Cole Porter's "Night and Day" is one of the most perfect songs in existence. My first encounter with it was Frank Sinatra's Duets album. Then U2 covered it as a B-side on one of their singles. (here's a live version of it: http://www.youtube.com/watch?v=oymNbCTZDAc) For the longest time U2's version was my favorite but lately, Maude Maggart's short and somber reading of it has become a favorite. I'm a sucker for strings.
: - Night and DaySweet Despair