Here's a version by Leann Rimes that could break your heart with its beauty
http://youtube.com/watch?v=iT88jBAoVIM&feature=related
Here's "Summertime" by a few different people:
http://youtube.com/watch?v=1yKgAEkCKxY (Ella Fitzgerald)
http://youtube.com/watch?v=mzNEgcqWDG4&feature=related (Janis Joplin - I saw her do this at the Filmore East - Amazing!)
I better stop - there are just too many versions of both of these songs!
Just one more - "Danny Boy," also by Elvis
http://youtube.com/watch?v=XaBHtfMLhs8&feature=related