I have a strange fondness for extreme metal cover versions of popular songs. Sometimes they work really well; sometimes, you wonder what the cover artist was thinking when they recorded the song.
Here's one I like: it's Led Zeppelin's 'Kashmir' by a Czech band called Silent Stream of Godless Elegy. They play doom metal influenced by Moravian folk music and deserve a wider audience.
Survivor's 'Eye of the Tiger' by Withering, on the other hand, is not so good. A rock anthem with growl vocals just sounds, well, silly. I should point out that Withering, a death/doom metal band from Finland, are actually pretty good. They're not unlike Insomnium, a favourite band of mine. (I've seen Insomnium live twice, and they were excellent on both occasions.)