Wierd Al - Smells Like Nirvana
Wierd Al - The Saga Begins
Mason Williams - Classical Gas
Metallica - Enter Sandman
Spider Robinson - The Drunkard's Song (may not count; not well known at all. But I like it, dammit.)
E Nomine - The Lord's Prayer
Wierd Al - Enter Napster
Queen - Bohemian Rhapsody
Monty Python - The Idiot Song
... I have an interesting collection of music, no?