When choosing to what Coldplay Scientist cover to listen to, go with the Aimme Mann one because Willie Nelson and his voice is a letdown.
In the meantime, here are some of my other favorite female sung covers:
Colin Farell's ex sings a Smiths tune (Much better than it sounds, believe me)
Neko Case sings some Tom Waits, probably far better than Scarlett Johansen
Sia sings Radiohead, although here, the violins are the standout part.