I don't have time to read through all the posts here, but thought I'd throw this out for what it's worth — pardon if someone's already mentioned it.
How 'bout Ray Stevens? He's an absolute musical genius and he parodies EVERYTHING. His parody of Pirates of Penzance is a scream and what he does to the Michael Jackson (now tell HE is begging to be parodied!) song Bad would probably give a sheep lover a woody.
And what about Tom Lehrer (Sp?). He parodied all kinds of things.
Low humor? Not if it's done well.