The Elvis version:
The Willie Nelson version:
The Pet Shop Boys version:
And just for kicks, Tom Chaplin's (from Keane) impression of the Pet Shop Boys' version (fast forward to 6:03, but start at 5:15 to get the context...or maybe watch the whole thing for even more context)
All in all, I think I like the Pet Shop Boys version best, but Elvis' has a quality that I love and that isn't really captured in the PSB version. Willie Nelson, meh. And Tom Chaplin is just silly.