The Myers Briggs Type Indicator (MBTI) is pretty popular and most people in my seminars and coaching programs report having taken it at least once. Here are some helpful resources to help you use the 16 type framework more effectively.
Check out this tool which gives you a quick overview of all 16 steps. You can use it as a way to speed read your team members when they tell you their type. http://www.mbticlub.com
I also subscribe to the MBTI Blog and enjoy the comments. For example, a recent exchange discussed how some people consider themselves introverts in face to face interactions and extroverts when using social media. Is Twitter more extrovert or introvert friendly? Fun stuff!