I've found the SM57 versatile enough to switch from voice to whistle to clarinet - or from fiddle to crwth to kemence to zither causing the minimum headaches to the soundman. In quick on-off festival sets this is pretty essential when sound-checking time is limited / non-existent.

What's that American band who only use the one lovely big mic on stage for instruments, vocals & all? I'd love one of them.