Here are some links for further reading:
http://www.keirsey.com
http://www.personalitypage.com/portraits.html
http://www.typelogic.com/fa.html
http://en.wikipedia.org/wiki/Myers-Briggs_Type_Indicator (MBTI on wikipedia)
http://en.wikipedia.org/wiki/Keirsey_Temperament_Sorter (the 4 temperaments on Wikipedia)
