Omnigraffle +
USITT stencils
Big caveat, I don't know many professionals (at least NYC Sound Designers) who actually use the
USITT drafting standards. Most of us use Omnigraffle, some use
Vectorworks for it but I think those people are crazy.
I think a lot of us pull ideas from the standards but have found ways to make them work for us in more intuitive ways, it's an ongoing conversation in the city (I know
TSDCA has brought it up at a few of their meetings).