One of my greatest struggles as an artist is believable anatomy and dynamic figures. Since humans can take on insane poses, even ones that aren't contortionists, I look for references like mad. So as I had quite the time looking for them, I'll share what I have so that you don't have to look all over God's green Earth for them.
Here's one to start off.
posemanics.com is a friendly little sight that provides you with many poses to work with, free of charge. All the pose people are skinless, which can be a little unnerving, but that makes them less bothersome to work with in public. Artists already get enough weird looks simply because they are, we don't need anymore reasons for people to think we are weird by flaunting naked people on the computer screen. The "models" come in female, male, male bodybuilder and child.
The only draw back I see is that at times the models can be stiff as they are renderings rather than real people (which is why they can be skinless...). The fact that each pose can be rotated 360 degrees makes up for this in my opinion and often when I've used these as reference my hand loosens them up as I draw so its not too big a deal. There is also an iphone app that allows you to view the poses on the go, but since I have no iphone, its sadly useless to me. I wish it was for other phones as well. All in all though, its a nice site to have on hand.