I'm 50/50 on cover songs. It all depends on the song, the artist, and whether it's an exact copy or a totally new rendition. True, there are few that are better than the original, but those that are tend to be truly great. For example, do you remember the original version of "Hey Joe" by The Leaves? Or the cover version by Jimi Hendrix? I've never even heard the original. "Hurt" by NIN basically became Johnny Cash's song with the version he did.
Didn't see this one posted, but I think I saw it on the sad songs thread. Originally by Tears for Fears: