When I used to draw a lot my main subject was human form/anatomy, as such my main sources where medical books, sculptures, life drawing groups and lastly my favourite source was 5 cd's by a guy named Riven Phoenix.
you can see his website here
Learn To Draw The Human Figure
He teaches you how you can draw an anatomically accurate human from your memory.
Now you have to buy the cd's, although when I found his cd's they were all free on places like youtube, but I still bought them to help support him.
If you have some money for it I'd definatly recommend getting them if you are interested in drawing the human figure. They help out a lot.