Here you can find links to other websites with the topic "Cover Songs". If you know a site which is worth to be taken in this directory, write an email to me.
SecondHandSongs provides a huge database of songs and cover chains. Very good ressource.
A list with 50 cover versions and comments about the songs. But if they are really the 50 best cover songs is of course a matter of taste.
Great Italian website about cover songs and Italian cover bands.