Nivaran's 'Man who sold the world' is great. My favourite version.
I prefer Robert Plants version of ' If I was a carpenter'
I love Ugly Kid Joe's cover of Cat's in the craddle.
Although I adore the original 'Turn the Page' by Bob Seger (how can you not?) my favouritre version is by Metallica ( although the video really upset me tbh)
I agree with the others who have suggested 'Wicked Game' by Him (although HIM are rubbish live it has to be said!)
Marianne Faithfull's 'Working Class Hero' spits venom! Brilliant!!
U2's 'Helter Skelter' is pretty good for U2!
I love Korn's 'Word Up' to Cameo, although I did like the original.
Metalliac's version of Whisky in a Jar is 1000 x better than Thin Lizzy's whose own version was better than the Dubliners! ( although I doubt James Hetfield and others knew where the Cork and Kerry mountains were!! 
Although not better but definatly different I do enjoy comfortably numb by the Sissor Sisters. I have both versions.
I prefer Cyndi Laupers ' I drove all night' to Roy Orbison.
so many songs I could go on all day!!