I just discovered this a couple of days ago, and it is really brilliant. It's a "3D-modelling" program called
Make Human.
I suppose it's not technically a modelling program, as you are not really building or modelling anything. It does exactly what the name says: makes a human. You start with a generic and genderless human mesh, then you adjust the features; masculinity/femininity, height, weight, muscles mass. Then you can go into more details, all the way down to facial features.
The part I like the most is that you can pose the human in any way you like! The joints look a bit odd, but for just getting the proportions, perspective and angles right, it's brilliant.
I highly recommend trying it out. Saves searching for that perfect pose reference, which you never really find anyway. Make Human is an open source program, and is completely free. It is still in alpha, but works fine. You can even import the humans you make to a 3D-modelling program like Blender if you like, and continue working on them from there!