I'm always fascinated when I find really fantastic information about the human figure in completely unexpected place.

Stratz's books don't appear to have ever been published in any other languages besides German, and his works don't appear to have experienced much popularity outside of Germany. Wikipedia, for example, does not have an English-language page on him, though there is a decent size entry on him on the German version of Wikipedia (english translation).
As a result, finding his books in the English language is practically impossible. But, from what I've read, much of the prose is essentially valueless, filled with outdated science and bunk pseudo-science in the form of "physical anthropology". But, apart from the words, there are literally dozens of illustrations and photographs from his books that have value to figurative artists, including many line drawings showing proportions as well as nude photographs of people of all ages from literally all over the world.
Since Stratz's books were all first published before 1920, they are all in the public domain in virtually every country in the world, meaning his works can freely be copied, republished, or used. Wikimedia Commons has some of his books (Der Körper des Kindes und seine Pflege, Die Fraunkleidung, and Die Körperpflege der Frau), and Google Books has several other of his books available. The Internet Archive also has several of his books digitized.
Here is just a tiny sample of images from his books:






Link: http://www.makehuman.org/blog/index.php
I recently discovered a very fascinating open source software project called the Make Human Project. It's been around since 2001, but I only heard about it recently. As a programmer and sculptor with a fascination with anatomy and the sheer diversity of the human form, this is right up my alley.

The goal of the project is to create a single mesh — a 3D representation of a person — that can be transformed (or morphed) into any possible human shape, regardless of age, ethnicity, level of fitness, or other individual factors. But the project is not only about making a mesh, it's about a whole platform - a computer program to allow you to modify the mesh with intuitive controls (without needing to know how to sculpt in 3D). The program will allow you to create a base 3D model to represent any individual, real or imagined, and export that figure to be used in other programs, or Make Human can render images itself.
The program is still in alpha (early testing with features still under development) and there are many features that aren't available yet (hair, the ability to pose the figure, the ability to generate low-resolution models for games, clothes), but the results are still impressive. Since Make Human will export files in a widely-used, industry standard file format called Wavefront OBJ, you can use the program today as a starting point for digital sculpting, finishing up in another program like Maya or Blender.
Because the program is open source, if you're technically minded, you can actually make changes to the underlying data models to suit your own needs, and if you're a competent digital sculptor, you might even consider contributing to the project as an artist.
When you first launch Make Human, you're presented with the "universal mesh". This figure is designed to be completely androgynous, with features that are completely ethnically neutral:

There are four sliders on the left side that allow you to mix different full-body features. Move the top slider to the left and the figure becomes more feminine, to the right it becomes more masculine. The second slider changes the apparent age from the figure from twelve to seventy. The third and fourth sliders let you adjust the weight and muscle tone of the figure. Here's an example of the female figure in Make Human age progressed from 12 to 70.

On the right side of the screen, there are four maps that contain ethnic morphs. These contain morphs with facial features common to certain geographic areas and/or among certain ethnic groups. Although this feature is still under development, it's amazing to see the variety of human features that they've captured already. They've got six major ethnic targets from Africa alone. And these targets are not all-or-nothing. They can be mixed and matched, so you could create a figure with features that were, for example, partially Koisan (an ethnic group from the southern part of Africa) and partially Sudanid (ethnic group dominant in the Northeast of Africa).

Although there are fewer ethnic targets for Europe and Asia and none yet for the native American populations, I've spoken with the project members and expanding the ethnic targets is one of their highest priorities. They are actively recruiting digital sculptors and creating composite reference images of the different ethnic groups.
If this were the extent of Make Human, it would be impressive, but it's not. You can also modify the attributes of specific portion of the body, both on a macro level (leg, pelvis, upper torso) or on a micro level (belly button, clavicle, etc). Do you want long legs, or a short neck? No problem. Want a fat figure with muscular arms? Again, no problem. Long torso, big feet, off-center belly button? Want a pretty girl's head on a muscular man's body? All okay but, ummm... you might want to talk to a psychiatrist about that last one.
The roadmap for Make Human is fascinating. They have plans for adding pose tools, different emotions, clothes, different shaders, more textures (skin types), low poly exporters to allow making figures for games. When completed, it's going to be an amazing program. Scratch that - it already is an amazing program. When it's done, it's going to be phenomenal.
If you've got a few minutes to spare, you should download the current alpha and try it out. If you've got a little more time to spare why not consider contributing some of your time to the project (if you can't, you could also donate some money). This is a community-based project, which means that nobody is paid to work on it, and nobody has to pay to use it. It is, and will remain free.
Here's an interesting website I found while browsing museworthy called The Great Nude. The site has a number of interesting initiatives, including The Great Nude Project, which is a series of videos where the artists behind the site recreate famous works of figurative art using a model, and Sketch Sessions, a series of videos where they show artists working from live models.
This is definitely a good resource to bookmark if you're into figurative art, though so far, it's all two-dimensional work, no sculpture.
I'm about to state the obvious here, but just for the record, the links above both contain nudity. So far, I've only seen female nudes on the Great Nude website. I'm not sure if that's their focus, or if there will be male models used in future videos.
Link: http://ajuss2007.googlepages.com/propaganda.html
I stumbled across this fascinating page today. It's a collection of scans from Soviet-era anatomy books.
Google is hosting the Life Magazine archives for free. That means you can view, in moderately high resolution, and search the entire contents of Life Magazine's extensive mulit-million photograph collection. Photographs published from the 1860s through the 1970s are available, and there's a lot of really great stuff in there, including a lot of potential reference material.
The first thing I did, of course, was to see what kind of photos they had on sculptors and, surprisingly, they had quite a bit. A lot of the sculptors covered were "modern", but there were a great many sculptors of note covered, including Henri Matisse and Henry Moore, to name just two.
The images are tagged, similar to the way Flickr tags their images, so I found myself jumping from topic to topic as I clicked tags. Be careful with this - you could easily lose a few hours to it.
One thing that struck me is that the magazine became much more conservative as time went on. I tend to think of the American public being on an ever-increasing trend towards being more accepting and more liberal when it comes to the body, but I know that's not true. I can't think of a better barometer of the public temperament than Life magazine, and this concrete proof showed me just how poor my perception was in that respect: There has most definitely not been a straight-line progression when it comes to acceptance of the human body in mainstream art.
In covering the arts, there are many photographs in the Life archives that were published from the 1920s through the 1940s that contain nudity. After that, they mostly dry up. By the 1950s, almost all images with nudity are shot in a discreet manner.
In an interesting bit of "meta" I came across in my search results, the archives contain extensive pictures from an article they did on Ezekial Candler Gathings, a representative from Arkansas. Unfortunately, most people don't know about Gathings.
About the same time that Joseph McCarthy was leading our country into a witch-hunt against Communists and other undesirables, Gathings was convening a house sub-committee to investigate "subversive" and "anti-American" literature, which became known as "The House Committee on Current Pornographic Materials", but was usually called "The Gathings Committee". Most of what they went after were books that were overtly sexual, or those that discussed illicit drug use.
Although the First Amendment meant that Congress couldn't directly outlaw books and expect those laws to pass Constitutional Muster, they found a way to side-step the Constitution. They implemented postal regulations that made it a federal crime to send, via the mail, materials that had photographs of genitals or pubic hair. It wasn't a law, technically speaking, and they weren't outlawing the material, so they expected it to work. And it did. The regulations stayed in place until 1968. As a result, from 1952 until the late 1960s, most mainstream magazines were extremely conservative when it came to using nude imagery.
Anyway, as a celebration of what has been lost in this country thanks to interfering busybodies like Ezekiel C. Gathing, I present just a sampling of photographs from the Life Magazine Archives that feature nudity. All images © Life Magazine and hosted by Google.