I discovered it through Rod Stewart's unplugged version. His raspy voice has never left me unmoved. :)
Another Stewart's version exists with Jeff Beck, here in 2009.
Al Green's is great, isn't it ?
Joss Stone's among the recent versions:
Aretha Franklin's is a classic, she takes her time to make the music resonate. :)
And men and women together here with the Staples Singers:
More on the context of the song.