Here is a great online resource for body language and interpretation of positioning.  And, best of all, it's free:

http://www.center-for-nonverbal-studies.org/6101.html

And here is one for Semiotics, the language of symbols and interactions:

http://www.aber.ac.uk/media/Documents/S4B/semiotic.html

These are great primers for anyone interested in messag, content, intent, all that stuff.