Beatrice de Gelder has a nice webpage with many free PDFs of her peer-reviewed work on what she calls EBL -- Emotional Body Language. I haven't read through it all, so we'll see how much "newz u can uze" it contains.
Flipping through some review articles, though, it seems that we're not at the same stage of understanding how emotions are expressed by body language as we are for understanding how they're expressed by the face, where Paul Ekman and his colleagues have broken down the nuances of human emotion into fine-grained analysis of muscle movements. At least it looks like the research has been picking up within the past five years.
One neat finding: people notice when the emotion conveyed by body language doesn't match that conveyed by facial expression. For instance, it's jarring to see a figure with their arms back and shoulders pointed forward, as though they were angry, while their face has the eyebrows pointing upwards, as though they were afraid.
I mention this since pickup artist enthusiasts write a lot about body language, but if it is not congruent with facial expression, people will probably notice this and think the person is lying. They need to work on controlling their face too. I'm actually surprised that pickup artists haven't bought Paul Ekman's facial expression analysis kit and incorporated some of its basics into their knowledge base -- since the science is light-years ahead of the study of body language, you'd likely get more out of it. You'd be more aware of how to fake certain emotions, as well as read the emotions of others.