I've seen a number of tutorials on proportions over the years, and have some in a couple books even, but something just is not clicking with it.
Part of it is that most of what I see is the generic "x number of heads high" tutorial, which may cover the front and side in many cases, but they are generally tailored for realistic or similar design.
I can go and draw out the lines many times over, and will get the proportions of a character looking somewhat OK, but characters are a lot more interesting if they do something other than stand straight while facing you.
This is where things *really* break down for me. As much as I've worked in 3D and as long as I've sketched stuff in 2D, it's still hit or miss if I get proportions close enough to be usable.

Are there any decent books or online tutorials that go into proportions of the human form in depth, going beyond "this is what we look like from the front and side"?

Much like the use of a persons head size as a guide, I am looking for some methods of creating guides for myself that will help me judge the length needed for various positions.

Proportions are something that have been such a problem for me, that I'm actually better with hands and feet than bodies, which is scary considering the amount of trouble I hear that people have with hands/feet.