EXTREMELY useful site.

POSE MANIACS

They offer 3D models you can look at through your browser in all kinds of poses and perspectives, so you can get a better idea of how human form works. On top of that, you get to see them down to the muscles, allowing you to get the shapes and lines just right.

They also offer a Negative Space view, Hand modeler, Perspective editor, and if you're interested, a 30 second drawing application. If you need a static human reference, this is the site to go to.