Any of the Ruins' medlies. I guess they aren't cover "songs" in the strictest sense but they do contain little bits of songs by other artists. Their version of "Sabbath Bloody Sabbath" in "Black Sabbath Medly Reversible" is SOOOOOOOOOOOO much better than the original. It's utterly hilarious. All throughout that song, they sing Ozzy's vocal melodies but in their characteristic maniacal yodeling voice without any of the original inane lyrics. The lyrics are instead replaced by the gibberish syllables that they use in place of words. My former roommate was driving us down I-76 to his new place and when that track came on, he almost killed us from laughing so hard while driving. Their prog and Mahavishnu Orchestra (with Sasaki soloing on bass like John McLaughlin did on guitar!!!) medlies kick ass too.